Can You Work Out The Angles In This Triangle?

Geometry Level 1

Three angles of a triangle are in a ratio of 4:7:9.
Find the sum of the smallest and the largest angle of the triangle.

117 81 20 99

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18 solutions

Discussions for this problem are now closed

Sanghamitra Anand
Dec 26, 2013

Consider the unknown angles as 'x'
Therefore, 4:7:9 becomes 4x: 7x: 9x.
Since, the sum of the angles of a triangle is 180°,
4x + 7x + 9x = 180°
20x = 180° (add the like terms)
x = 180° ÷ 20
x = 9
Therefore, by sustituting the value of x, we get,
4(9) : 7(9) : 9(9) = 36:63:81
In this triangle, the smallest angle is 36 and largest one is 81.
Therefore, sum of these angles = 36 + 81 = 117
Thus the problem is solved!

we could have added the ratios (20)and done 4/20 180=36 and 9/20 180=81 and add it up!

shreesha shenoy - 7 years, 3 months ago

this is simple methods

Vishwas Kadam - 7 years, 5 months ago

Thanks for a easy problem.

Rhishikesh Dongre - 7 years, 1 month ago
Carol Ma
Dec 24, 2013

Assume the 3 angles are 4X, 7X and 9X (4+7+9)x=180 x=9 (4+9)*9=117

The ratio of the angles is 4:7:9, and the sum of the angles is 180°.So 180°=(4+7+9) units=20 units.

The problem is to find the sum of largest and the smallest angles. We need to find the value of (4+9) units=13 units.

13 20 × 180 ° = 13 × 9 = 117 ° \frac {13}{20}×180°=13×9=\boxed{117}°

A Former Brilliant Member - 7 years, 5 months ago

i agree with your solution!

Elton Jay Pasco - 7 years, 5 months ago

sum of the ratio is, 4+7+9= 20 since the sum of the three angle is 180 degree then, the smallest angle is, (180 (4/20))= 36 the largest angle is, (180 (9/20))= 81 the sum is, (36+81)= 117 (ans.)

Rubel Haque - 7 years, 5 months ago
Eunice Stars
Dec 27, 2013

a 4 \frac{a}{4} + b 7 \frac{b}{7} + c 9 \frac{c}{9} = a + b + c 4 + 7 + 9 \frac{a+b+c}{4+7+9} = 180 20 \frac{180}{20} = 9 --->a= 4 × 9 4 \times 9 =36 ; c= 9 × 9 9 \times 9 = 81. So my answer is "" 36+81=117"" .

Sharath Chandar
Dec 26, 2013

4x + 7x + 9x = 180 (Angle sum property of triangle)

x=9

4x=4*9=36 (Substituting 9 to x)

9x=9*9=81(Substituting 9 to x)

SUM= 117

4X, 7X and 9X (4+7+9)x=180 x=9 (4+9)*9=117

Khalid Guro - 7 years ago
Prasun Biswas
Jan 2, 2014

Given that the ratio of the angles are 4 : 7 : 9 4:7:9 , so let us take the angles as 4 x , 7 x 4x,7x and 9 x 9x .

Now, we know that sum of all the angles of a triangle is 180 ° 180° .

So, 4 x + 7 x + 9 x = 180 20 x = 180 x = 9 4x+7x+9x=180 \implies 20x=180 \implies x=9 .

Now, Sum of the smallest and largest angles = 4 x + 9 x = 13 x = 13 × 9 = 117 =4x+9x=13x=13\times 9=\boxed{117}

Anthony Flores
Dec 29, 2013

4x+7x+9x=180 => x=9 13x=13*9=117.

Raj Gobal
Dec 27, 2013

the sum of 4 ,7 and 9 will be 20. as we know the total interior angle of a triangle is 180 degree divide 180 degree by 20 and u will get the value of one part. then total up the product 4 and 9 and the product of 9 and 9 u will get the answer 117

Queen Ang3l
Dec 27, 2013

4+7+9=20

4/20 * 180=36

9/20 * 180=81

36+81=117

Tarang Saluja
Dec 27, 2013

4x, 7x, and 9x are the measures. That means that x is worth 180/20 = 9. So the largest and smallest add up to 13x, so that means 9x13 = 117

Devjeet Baghel
Feb 10, 2014

Three angles of a triangle are in a ratio of 4:7:9.

let the ratio be x

4x + 7x + 9x = 180 (the sum of all the three angles in a triangle is 180 )

20x = 180

x = 9

the first angle = 4x = 36

the second angle = 7x =63

the third angle = 9x =81

the sum of the smallest and the largest angle of the triangle. = 36 + 81 = 117

Mandar Deshmukh
Jan 19, 2014

let the common multiple be x so 4x +7x+9x = 180 x=9 therefore angles are 36 63 n 81 so ans is 117.

Henry Okafor
Jan 17, 2014

The sum of ratios of the sides is 4 + 7 + 9 = 20.

The smallest angle is 4 20 \frac{4}{20} * 180 = 36 since 180 is the sum of interior angles of a triangle.

The largest angle is 9 20 \frac{9}{20} * 180 = 81

Hence,the sum of the smallest and largest angle is 36 + 81 = 117 degrees.

Marcos Lima
Jan 1, 2014

If we have the ratio 4:7:9 and that the sum is 180, so there is a number n that satisfy: 4n+7n+9n=180, n=9, the largest angle is 81, and the smallest is 36. In this way, we have the sum 117.

Ammar Mohammad
Dec 31, 2013

Let 4x+7x+9x = 180 20x=180 x=9 The smallest angle = 4x9 = 36 The largest angle = 9x9 = 81 The sum of smallest and largest angle = 36 + 81 = 117

Jack Weinstein
Dec 29, 2013

The sum of all angles in a triangle must always equal 180°, so by adding up the ratios (4+7+9) to get a total of 20 and dividing the total internal angles of the triangle (180/20=9) we know what the ratio of each angle is (36:63:81). Then we just add up the largest and smallest values (36+81=117).

Sọc Chính
Dec 29, 2013

The sum of the three angles of a triangle is 180. Because the ratio of the 3 angles is 4:7:9 and we need to find the sum of the smallest and the largest angle then the sum should be equal to 180.(4+9)/20=117

Luke Limbo
Dec 27, 2013

You have to represent each element by 'x' then add and equate to 180. 4X + 7X + 9X = 180 20X = 180 X = 9 then substitute '9' to the X of 4 and the X of 9 multiply and then add. 4(9) + 9(9) 36 + 81 = 117

Budi Utomo
Dec 26, 2013

Triangle has 180 degrees of angles. So... we must know if 4 : 7 : 9 = 4x : 7x : 9x ---> So, the sum of the smallest and the largest angle of the triangle = (4x + 9x)/(4x + 7x + 9x) * 180 = 13x/20x * 180 = 13/20 * 180 = 9 * 13 = 117 Degrees. ANSWER : 117

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