Sum The Grey Angles

Geometry Level 1

In the image above, what is the sum of the grey angles (in degrees)?


The answer is 360.

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66 solutions

Discussions for this problem are now closed

Chinmay Raut
Jun 2, 2014

Relevant wiki: Triangles - Angle Sum

Notice that the three triangles are joined at the base. If we call those 3 unshaded angles x , y , z , x,y,z, we know that x + y + z = 180 x+y+z = 180 since they form a line.

The sum of all of the angles in the 3 triangles is 3 180 = 540 , 3\cdot 180 = 540, and the sum of the unshaded angles is 180. 180. Thus, the sum of the grey angles is 540 180 = 360. 540-180 = 360.

Sum of angles of three triangles is 540, minus the supplementary angle made by the three not shaded angles which is 180 is 360 degrees. :)

Jessica Cas - 7 years ago

3*180 - 180(sum of unshaded angles) = 360

Anshul Goswami - 7 years ago

Very Nice solution

Shankha Das - 5 years, 8 months ago

180+180+180[3 triangles ] -180 [unshaded] =360

Saikumar Gunishetty - 7 years ago

The sum of 3 angles minus the the angles that would form a line angle and that would be equal to 360.

Matthew Franz Oco - 7 years ago

its very simple... Two rules are being applied. Rule 1) Sum of all the angles of a triangle is 180,,,,, so sum of all the angles of these three triangles will make 3*180=540.

Rule 2) A straight line makes an angle of 180,,,,, so the sum of unshaded angles will be 180.

So subtract the unshaded angles (180) from the total (540) i.e. 540 - 180 = 360...... simple :-)

Muzzammil Hashmi - 7 years ago

Summation of interior angles of a closed polygon is equal to (number of sides - 2): (6 - 2)(180) = 4 (180) = 720 Now , less the two straight lines which is equal to 180 each, so 180 x 2 = 360, Then, 720 - 360 = 360 degrees <--- answer

Crisjay Grecia - 7 years ago

Good. (n-2)180 -(180 *2)=360

Prasad Imm - 5 years, 6 months ago

We know the sum of angles of triangle is 180, i.e (3*180=540). But removing the straight angle we get, 540-180=360...

Samrat Hasan - 7 years ago

180+180=360

Ralph Mercado - 7 years ago

(3x180)-180=360

Idrak Khan - 7 years ago

very nice and easy explanation.thanks.

Prasad Imm - 5 years, 6 months ago

very good....... nice.....

Shubham Singh - 5 years, 4 months ago

sum of angles in a traingle is 180 .there are 3 triangles.sum of these 3 triangles is 180+180+180.but there is straight 180 degree line .excluding that we get 180+180=360.

Sai Charan Dasari - 7 years ago
Amlan Baishya
Jun 5, 2014

The overall shape is a hexagon. The sum of all corner angles is 720. In this case 2 straight angles are missed out in the 1st and 3rd triangles. Hence, the required sum is 720 2 × 180 = 360. 720 - 2\times 180 = 360.

Same idea, irregular hexagon which has 720' and missing two 180' (360'), 720 - 360 = 360

Ah Pang - 7 years ago

Just notice that the mid triangle line is parallel to the base. And so the lower side unshaded angles shall be equal to shaded angles in middle triangle respectively. SO the question becomes the sum of all angles (shaded and unshaded) of right and left triangle=2*180=360

Ashutosh Jha - 7 years ago

That's what I did straight away!

Billy Butler - 5 years, 7 months ago

Let the angles of the 1st triangle a , b a,b , the 2nd c , d c,d , the 3rd e , f e,f , and let the remaining angles of the 1st,2nd,3rd as x , y , z x,y,z . Now we want to find a + b + c + d + e + f a+b+c+d+e+f .

We see that a + b + x = 18 0 a+b+x=180 ^{\circ} (1) because the sum of angles of a triangles is 180 degrees.

This also comes with c + d + y = 18 0 c+d+y=180^{\circ} (2) and e + f + z = 18 0 e+f+z=180^{\circ} (3) for same reason.

We also see that x + y + z = 18 0 x+y+z=180^{\circ} (4) because the measurement of a straight angle is 180 degrees.

So you can use these information to find the gray angles.

Let's go ahead and sum (1), (2), and (3) we'll get...

a + b + x + c + d + y + e + f + z = 18 0 + 18 0 + 18 0 = 54 0 a+b+x+c+d+y+e+f+z = 180^{\circ}+180^{\circ}+180^{\circ} = 540^{\circ}

Substituting (4) and we get a + b + c + d + e + f + 18 0 = 54 0 a+b+c+d+e+f+180^{\circ} = 540^{\circ}

Therefore a + b + c + d + e + f = 36 0 a+b+c+d+e+f = \boxed{360^{\circ}}

Let the three un-shaded angles around the common vertex be X, Y and Z from left to right.

In the left most triangle, the sum of shaded angles = Y + Z

In the middle triangle, the sum of shaded angles = X + Y

(In the above case, use exterior angle theorem and use the fact that vertically opposite angles are equal.)

In the right most triangle, the sum of shaded angles = X + Z

Therefore, sum of all shaded angles = 2(X + Y + Z)

Now, X + Y + Z = 180

sum of all shaded angles = 2(X + Y + Z) = 360

Nithin Krishnan
Jun 4, 2014

Quite Simple,

Using: 1) Angle Sum Property says that sum pf all interior angles of a triangle is 180. 2) Angles on one side of a straight line will always add to 180 degrees.

Sum of all angles of the 3 triangles = 3*(180) {Using 1} Sum of the pending non gray interior angles of the 3 triangles = 180 {Using 2}

So, the Sum of gray angles = 3(180) - 180 = 2(180)
= 360

the base line of the two triangles and the base line of the inverse triangle are parallel, the shaded angels on the inverse triangles are equal to the non-shaded angels on the base line, so all shaded angels are for two triangles >>>> angles Sum =360

They need not be parallel

Meenakshi Janardanan - 7 years ago
Parth Satasiya
Mar 12, 2016

Suppose 60*6=360

Filipe Amaral
Jan 14, 2016

Need to say that the base of the middle triangle is paralel with the basis of the other two triangles!

Wyatt Kachner
Jan 2, 2016

This is not the most robust method, but one of the quickest. I took the basic geometric rule that the sum of interior angles of a polygon is equal to 180(n-2), where n is the number of sides. So the sum of angles is 720, but there are two places where part of that sum is left out of the red. Fortunately, both of those places are straight lines on the interior, so they are each 180 degrees and add up to 360. Subtract 360 from 720 and you get 360. The answer is 360. The drawback to this approach is that you must know and understand the base formula for the interior angles of a polygon, and there are similar questions which may have a larger complication than simply subtracting 2(180) from the total.

the upside down triangle is irrelevant, all you need to know is that there are two triangles, since each one has 180°, the sum of both triangles is 360°

Vino Vishwa
Dec 4, 2015

All the triangles are placed in the base line so the line angle is 180° The of triangle angle is 540° We subtract 540-180 =360° Therefore the sum of the triangle is 360°

The three angles in the bottom form one 180° angle.. Sum of 3 angles in one triangle is equal to 180°. We have 3 triangles here, so from here it's easy to get the formula: 3n-n => 180*3-180=360

Christopher Unrau
Nov 16, 2015

If we take the three angles that are not included, we can see simply they equal 180 degrees. Because there are three triangles, we can say that the sum is equal to 3(180)-180, or 2*180. This is 360 degrees.

Achille 'Gilles'
Nov 16, 2015

See all the triangles with the same height while keeping the same angle ratio... the figure become a quadrilateral and apply:

"The interior angles of a simple quadrilateral ABCD add up to 360°."

"

Siva Meesala
Oct 5, 2015

Here three triangles are there .required sum of angles is equal to 3 (180)-straight angle180.then it is 360

Rizza Cordova
Sep 8, 2015

looking at the triangles, I just figured this is an equilateral triangle. so this means 60 degrees per angle. 60*6 = 360.

Adarsh Mahor
Jul 17, 2015

There are 6 angles So it forms 2 triangle So 1 triangle=180˚ So 2 triangle=180*2=360˚

Ryann Laurezo
Jul 11, 2015

observed the three unshaded angle, it is equal to 180 degrees. so just multiple 3*180 -180 which is equal to 360.

Jazz Nash
Jul 8, 2015

The sum of interior angles of all triangles equal 180. So 180° * 3 = 540°. Now because the 3 triangles meet at one point, their corners (unshaded) form a straight line which equals 180. With that, 540° - 180° = 360°.

Md Mehedi
Jun 29, 2015

6 angles are sum of 360. Middle angle is a straight line means 180 which contains 2 angles. Other 4 angles is the sum of 180. Total 180+180=360

Ahmed Obaiedallah
May 27, 2015

sum of internal angles of triangle =180

let the three joint angles to x, y, z together they form a straight angle

so x+y+z= 180

3 180 180 = 2 180 = 360 3*180-180=2*180=\boxed{360}

Mohammed Rasith
May 25, 2015

Sum of all the angles in a triangle will be 180. There are totally 3 triangles and the total angle will be 540.

To find the sum of gray angles, we can subtract the not shaded angles from the total. The not gray angles from a straight line. The angle for a straight line is 180.

So, subtracting 180 from 540 will be 360, the sum of all gray angles.

Osama Zahid
May 25, 2015

Sum of angles of three triangles is 540, minus the supplementary angle made by the three not shaded angles which is 180 is 360 degrees. :)

Vaibhav Borale
Jun 28, 2014

there are 3 triangles each having 180 deg sum considering all their angles. so, total sum of all the angles is 3*180=540

but, here don't consider those three angles which are not greyed....as they are forming straight line sum of angles is 180

thus all the angles which are greyed effectively gives addition of 360 deg

Adrian Ionescu
Jun 20, 2014

I think this problem could be made a little less obvious if the top middle line was not parallel to the bottom one, but at some angle.

Andrew Tiu
Jun 19, 2014

First we have to remember that the sum of a triangle's angles is 180 degrees. Seeing that the shapes in the figure are all triangles, we can count how many shaded angles there are, divide by 3 and multiply by 180. So: 6 shaded angles/3 = 2 triangles' worth of angles. 2*180 = 360 degrees

Sayed El Khatem
Jun 18, 2014

At first it looks difficult. But as you could see the sum of three triangles is 540 . and we could minus 180 (as the the sum of three angles at the same line is =180) so the result will be 360

Vachaspati Mishra
Jun 15, 2014

The total sum of angles in the three triangles is= 180 degrees*3=540 degrees. The sum of non-gray angles is=180 degrees as they lie on a straight line.Therefore sum of gray-angles is = (540-180 degrees)=360 degrees.

Yeasir Hridoy
Jun 15, 2014

The three triangles have 3*180=540 degree. The three unshaded angles make a straight line that is 180 degree. So the shaded angles have 540-180=360 degree

all of the triangles contain 180 degrees so multiply it by 3 then subtract the angle formed by the line which is joined by the 3 non shaded angles of the triangles which is also 180

Syed Ahsanuddin
Jun 12, 2014

Sum of angles of three triangles is 540, minus the supplementary

angle made by the three not shaded angles which is 180 is 360

degrees. :)

Saakshi Singh
Jun 11, 2014

There are 3 triangles and the unmarked ones form a straight line. All angles of straight line=180 Angle of three triangle=180×3=540 Therefore, dark angles=540-180=360

Eunice Saavedra
Jun 10, 2014

3(no. of triangles)x180(sum of angles in a triangle)-180(sum of non gray angles) = 360

Mihir Deshpande
Jun 10, 2014

consider the 3 angles in linear pair which are not sheded as x and y and z and the sum of all angles in a triangle is 180 as they are in linear pair. therefore 180 - x + 180 - y + 180 - z = sum of the required angles. 540 - ( x + y + z ) = Sum of grey angles. 540 - 180 . therefore its 360 :-)

Shivansh Tripathi
Jun 10, 2014

Since there are three triangles, therefore the total sum of angles = No. of triangles × 180 = 3 × 180 = 540 and as we put some logic in the problem we observe that we don't need to find the three angles from each triangle and that all these three angles lie on a straight line so we will subtract the sum of the three angles i.e. 180 from the total sum of the angles.Therefore, 540 - 180 = 360 , which is the answer.

Mufid Naufal
Jun 9, 2014

shaded angle = 180 + 180 + 180 - ( the sum of unshaded angle)

Ritesh Kumar
Jun 9, 2014

180 + 180 + 180 - ([a+ b+ c]=180) = sum of required angles = 360.

Devendra Sahasi
Jun 9, 2014

sum of all angle of triangles 180 + 180 +180 = 540

now minus 180 for all angles in straight line

540 - 180 = 360 degree :P

The simple solution is to consider the triangles joint at the base and to subtract 180 from the sum of the angles of 3 triangles, so 540-180=360

Ikhmal Fariq
Jun 8, 2014

as there is three triangles ... so calculate the total angle of all the triangle (180 times 3 ) = 540 ... the unshaded angle is 180 .. so 540 - 180 = 360

Hitoshi Yamamoto
Jun 8, 2014

x+y+z = 180 ; A = B = C = 180 ; (A-x)+(B-y)+(C-z) = 3A - (x+y+z) ; 3A - A = 2A = 360

any outside angle of a triangle is equal to opposite two angle inside the triangle. And sum of three angle in Triangle is 180. Thus got the result. But due to the fact that there are no labeling in the figure I am unable to explain it to the point.

Kanij Sharme
Jun 8, 2014

3*180 Degree=540 then,540-180=360,so answer is 360.

Rajat Kashyap
Jun 8, 2014

Let sum of grey angles in first triangle be A, in second be B and in third be C In Triangle first, unknown angle = 180-A Similarly, 180-B and 180-C in second and third triangle. Notice that, (180-A) + (180-B) + (180-C) = 180, which gives, A+B+C=360!

sum of 3 triangle's angles=540,then sum of the non-gray angles is 180 and finally sum is 540-180=360.

Rishabh Anand
Jun 7, 2014

this works out quite nicely. first, take a look at the right most triangle (you can do this with the others but i looked at the right most one). set the unmarked value equal to x, and the marked angles become 180-x. notice that the two unmarked angles of the other triangles are on a line with x, so they are also equal to 180-x. this means the sum of the marked angles is the sum of the angles of two triangles or 180 + 180 = 360

Ahmad Bashir
Jun 7, 2014

These are 3 Different triangles in shape and size.Considering the basic law that the sum of internal angles of any triangle is equal to 180.

Hence these are three triangles then there total sum sum would be, t1<180> + t2<180> + t3<180> = 540 degrees

Now as we can see the there a single vertice of all three of them where they all are meeting each other. We can see that the total angle of those three angles is eventually equal to 180.

As a straight line has an angle of 180.

For getting the sum of the grey angles subtract total sum of angles from the white angles from it,

G<> = S<540> - W<180> G<> = 360

Now that is your actual answer. :)

Mazaharul Haque
Jun 7, 2014

Alternate angles made between parallel lines are equal and sum of the angles of a triangle is 180. There are two triangles so after adding the angles it would be 360.

Sam Cheung
Jun 7, 2014

If you were to add up all the angles in the three triangles, you would get 540 degrees (3 x 180). Take away the unshaded ones, which happen to lie on a straight line (so = 180), and you get 360 degree.

الثلاثة زوايا الغير محدده تمثل زاوية مستقيمه 180 درجه إذن مجموع درجات الزوايا الملونة يساوى مجموع زوايا الثلاثة مثلثات مطروحا منه الزاوية المستقيمة (3*180) - 180 = 360

The 3 UN highlighted angles represent a straight angle with 180 So The sum of all colored angles = ( 3 * 180 ) - 180 = 360

Mohamed Abo-El Fadl - 7 years ago
Amit Yadav
Jun 6, 2014

Let say angles from right hand side a,b,c,d,e and f. Now, a+b=180-c and second equation , e+f=180-d. Add both equations

Rahul Patel
Jun 6, 2014

There we see 3 triangles. we know sum of interior angles of a triangle is 180 degree. so sum of angles of 3 triangle is 540 degree. also sum of angles made in a straight line on single point is 180 degree. so sum of gray angles is 540-180=360 degree.

Dyks Bronola
Jun 6, 2014

The sum of angles in a triangle is 180. The sum of angles of three triangles is 540 (3 x 180). The three unshaded angles lie on a straight line, which always add to 180. 540 - 180 = 360.

Junaid Hassan
Jun 6, 2014

(180+180+180)-180=360 as sum of angles of 3 triangles is 540 minus sum of angles on a straight line 180 equals 360

Diamantis Koreas
Jun 6, 2014

For the 3 triangles the sum of angles is 3* 180 degres but the white agles form a line, so 180 degrees. That means that the the sum of gray angles is 2*180= 360 degrees.

Osama Orsa
Jun 6, 2014

First understand the two basic rules of geometry… 1.The sum of all angles of a triangle is always equal to 180 degree. 2.Vertically opposite angles are equal.

Now, just consider right and left most triangles. Both have one unshaded angle and they have their vertically opposites angles (i.e shaded angles of middle triangle) which are equal to unshaded angles of right and left most triangles.

Hence all shaded angles constitute (are equivalent of) two triangles... that is 180 + 180 = 360 degree.

Arjun Chotaliya
Jun 6, 2014

all triangle are equilateral 60*60

Seriously?

Rodney Tabernero - 7 years ago

SUM OF ALL ANGLES IN A TRIANGLE IS 180 SUM OF TOTAL ANGLES IN 3 TRIANGLES IS 3X180=540 UN COLORED 3 ANGLES FORMED STRAIGHT LINE SO SUM OF UNCOLORED ANGLES IS 180 SO GREY COLORED ANGLES TOTAL = 540-180=360

Dario Sabate
Jun 5, 2014

Each triangle has 180 degrees, a straight line is also 180 degrees, hence 180*3(triangles) - 180 (straight line or unshaded angles) = 360 degrees.

Abo Maru
Jun 5, 2014

Its All rational ,assume,that every angle in three angles of triangle is 60, so ,we have here 6 angles ,6 60=360 ....... since they are connected by point that join angles ,so what increases in angle decreases in another,and the sum remain "CONSTANT"

Really? Why do you assume that every angle of the 3 triangles is 60? They need not be 60. There is no proposition saying that the 3 triangles are equilateral.

Rodney Tabernero - 7 years ago
Pooja Dutta
Jun 5, 2014

construction: just extend the straight lines and they act like two parallel lines cut by traversal. sole accordingly.

Not necesarrily. There is no proposition saying that they are parallel.

Rodney Tabernero - 7 years ago
Karen Vardanyan
Jun 4, 2014

Just notice that the two angles on the two sides of upper horizontal line are equal to the remaining (not shaded) angles of two triangles (the left and the right one) respectively. So the sum of shaded angles equals to double sum of a triangle. That's it. It was very simple.

Abdelrahman Azez
Jun 4, 2014

sum of the angles of the 3 triangles =540 the sum of the supplementary angles at the base =180 540-180=360=the gray angles

same way...

dhara jogi - 7 years ago
Chirag Tehri
Jun 4, 2014

60+45+120+90+45:360

How did you get these angles?

Micah Wood - 7 years ago

Exactly... how did you get them?

Karen Vardanyan - 7 years ago

wrong assumptions..

Orly Magpulong - 7 years ago
Krishna Garg
Jun 3, 2014

Since smaller and bigger lines( sorry ,names not given in the problem)and intesecting lines are making corressponding angles to complete the triangles.Each triangle will have total 180 degrees and so both will have toital 360 degrees Ans. K.K.GARG,India

Ryan Redz
Jun 3, 2014

3 triangles times 180 = 540 - 180(the 3 angles in straight line = 360

Another way to solve is to get the sum of interior angles of an irregular hexagon,then subtract the angle formed by two straight lines in the first and third triangle, Thus, S=180(n-2) =180(4)=720

Sum of gray angles=720-(180+180)=360 degrees

Gilbert Anota - 7 years ago

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