Tall, Tall Trapezium

Geometry Level 2

If each square has a side length of 1, what is the area of the blue trapezoid?

Note: A trapezoid has at least a pair of parallel sides. It is also known as a trapezium in the UK.

24 27 30 36

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21 solutions

Sravanth C.
Jun 1, 2015

There is a direct formula for finding the area of a trapezium, i.e. h × ( a + b ) 2 \dfrac{h×(a+b)}{2}

Where h = height = 6 units,

a= length of one parallel side = 3,

b = length of the other parallel side = 6 units

Therefore the area of this trapezium, = 6 × ( 3 + 6 ) 2 = 3 × 9 = 27 =\dfrac{6×(3+6)}{2} \\ = 3×9 \\ = \boxed{27}

I accidentally got this wrong because I assumed that the trapezium had the same slope on both sides, but here are my two cents:

Let A A be the area of the trapezium.

A = 24 + 3 = 27 \implies A = 24 + 3 = \boxed{27}

Brock Brown - 5 years, 11 months ago

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Well.. that is pretty nice....

Rishabh Tripathi - 5 years, 11 months ago

Nice explanation sir!

Sravanth C. - 5 years, 11 months ago

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Thanks. :)

Brock Brown - 5 years, 11 months ago

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@Brock Brown If you had assumed it to have different slopes, then you could have done, by splitting it into 3 3 rectangles too. Anyways it's a very good method!

Sravanth C. - 5 years, 11 months ago

That was freaking awesome...

Denste Varghese - 5 years, 5 months ago

Same way i solve this :)

Muhamad Ramdan - 5 years, 4 months ago

Good work...that's what I did. I wonder why there are so less solvers for this easy problem. I learnt this formula in my 9th standard.......

Debmalya Mitra - 6 years ago

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You still remember the formula, others don't :-)

Pradha Narasimhan - 6 years ago

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Thanks :-D

Debmalya Mitra - 6 years ago

there is an elementary approach without using the formula too.... This question is one which must be solved by everyone.. at least I think so.

Rishabh Tripathi - 5 years, 12 months ago

The area of entire square figure is 36, with each small square having an area of 1. We can find the area of blue colored trapezium by subtracting area with white color from 36. In the left side, there are 3 white squares and 6 partially white square region which adds up to 3 squares. There is another set of 6 partially white regions which adds up to 3 squares in right side.

36 - [ (3+3) left + 3 (right) ] = 27

Jeby Oommen - 4 years, 8 months ago

Area of square=36

Area of unshaded triangle on the left=6

Area of unshaded triangle on the right=3

36-6-3=27

Liam Magadia - 1 year, 1 month ago

6*(3+6)/2=18

Stef Copet - 5 years, 1 month ago
Ramesh Shanbhag
Jun 1, 2015

This trapezium has three parts (from left to right) - Part 1 - Haf of 12 squares (=6) + Part 2 - 18 full squares + Part3 - Half of 6 squares (3) = 27

That's one way of looking at the trapezium.

Chung Kevin - 6 years ago

yeah, did the same too

Jenny Lyn Gilbuena - 4 years, 3 months ago

Could you speak english please? I don't take forigin languge classes.

Jonathan Nayberg - 2 years, 8 months ago
Ben Fordyce
Jun 1, 2015

As you can tell off the bat the entire square has an area of 36 (6X6) except you are missing parts on the left and right. On the left you are missing half of a 1X6 column = 3, and on the left missing half of a 2X6 column = 6. Subtract to find the total: 36-3-6 =27

Different thinking and approach. .....I liked it.....

Istiak Reza - 5 years, 12 months ago

Ez learning... nice

Jonathan Nayberg - 2 years, 8 months ago
Maja Rada
Oct 13, 2015

What I did - split trapezium into three parts (from left to right):

  1. Right angled triangle nr.1 which has a surface: P1=2*6/2 =6
  2. The rectangle with surface of: P2=3*6=18
  3. Right angled triangle nr.2 and its surface is: P3=1*6/2=3

The end result (surface of the trapezium) is simply all these three surfaces added together:

P=P1+P2+P3=6+18+3=27

Dan Stols
Jun 21, 2015

The area of the triangles are (2x6)/2+(1x6)/2= 9. The square area is 36. 36-9=27

Odin Wang
Aug 10, 2020

Bottom base: 6 Top base: 3 Height: 6 Area of a trapezoid formula: height times (top base + bottom base) all divided by 2 Area = 27

One can use Pick's Theorem and count the number of points in the grid that lay on the border of the teapezoid (B), count the number of points that are in the interior of the figure (I) and use the formula:

B 2 + I + 1 \frac{B}{2}+I+1

Since:

B = 12 B=12

I = 21 I=21

The correct answer is:

12 2 + 21 + 1 = 27 \frac{12}{2}+21+1=27

Gia Hoàng Phạm
Aug 28, 2018

The area of the trapezium is h ( a + b ) 2 \frac{h(a+b)}{2}

Where h h is height which is 6, a a is p a r a l l e l 1 = 3 parallel_1=3 & b b is p a r a l l e l 2 = 6 parallel_2=6

So the area of the given trapezium is:

6 ( 3 + 6 ) 2 = 3 ( 3 + 6 ) = 3 × 9 = 27 \frac{6(3+6)}{2}=3(3+6) = 3 \times 9=27

Michael Schmahl
Jul 31, 2018

The formula for a trapezoid (U.S. English; trapezium in British English) is the easiest way to solve this, as other solvers have done.

But I want to introduce Pick's Theorem, which says that for a polygon whose vertices fall on an integer lattice, the area is equal to i + b 2 1 i + \frac{b}{2} - 1 , where i i is the number of lattice points in the interior of the polygon, and b b is the number of lattice points on the boundary.

To check, let i = 22 i = 22 and b = 12 b = 12 . Then i + b 2 1 = 22 + 12 2 1 = 22 + 6 1 = 27 i + \frac{b}{2} - 1 = 22 + \frac{12}{2} - 1 = 22 + 6 - 1 = \boxed{27} .

A = 1 2 ( a + b ) h = 1 2 ( 3 + 6 ) 6 = 27 A = \dfrac{1}{2}(a+b)h=\dfrac{1}{2}(3+6)6 = \boxed{27}

Ahsim Nreiziev
Mar 25, 2018

There are 2 ways to do this. Firstly, you can just count up the squares, with the central, rectangular portion being 18 unit squares. The triangular piece on the left is (1/2) of 12, or 6. And the other triangular piece is (1/2) of 6, or 3. That's 18 + 6 + 3 = 27

The other method is the trapezium formula. There are many equivalent ways to write down this formula, but the one that I found most useful for this problem is: (a + b) x h 2 \frac{h}{2}

With a and b being the parallel sides of the trapezium; and h being the height.

So, that's (3 + 6) x 6 2 \frac{6}{2} or 9 x 3 = 27

David Jones
Feb 4, 2018

Just to say, it's called a trapezium in the UK too.

Lyn Kolf
Jan 6, 2018

I counted solid blue squares. Looked at remaining squares and determined which squares would complete one solid square. These combined squares counted as a single additional square to the solid ones. So, I visualized the answer and got 27. No, I didn't print and cut anything out. Just looked at it a couple minutes.

Bhaskar Pandey
Oct 19, 2017

I will give a straightforward approach; By Pick's Theorem AREA of a non-intersecting planar graph =(No. of internal vertices)-(half of the no. of external vertices)-1

Jad Ghalloub
Aug 15, 2017

🔴Tips to solve this problem⤵️:

🔵What is the area of the big square: c✖️c=6️⃣✖️6️⃣= 3️⃣6️⃣

🔵What is the area of both white triangles:

🔘Area of the big one: Base✖️Height➗2= 2️⃣✖️6️⃣➗2️⃣= 6️⃣

🔘Area of the small one: B✖️H➗2=1️⃣✖️6️⃣➗2️⃣= 3️⃣

🔘Area of both white triangles: 6️⃣➕3️⃣= 9️⃣

🔵Required Area( blue trapezium )= Area of the square ➖Area of both

triangles=3️⃣6️⃣➖9️⃣= 2️⃣7️⃣

Dachi Tan
Sep 3, 2016

Break it into 3 regions: the left triangle (half of 6x2), the middle rectangle (6x3), and the right triangle (half of 6x1), the area is the sum of three: 0.5 6 2+6 3+0.5 6*1=6+18+3=27

Zaber Mahbub
Apr 21, 2016

It's not trapezium, it's trapezoid.

A quadrilateral who has two parallel and two non parallel sides is known as trapezoid.

A non standard quadrilateral is called a trapezium.

Area of trapezoid = (Sum of parallel sides)*(distance of parallel sides)/2

Area = (3+6)(6)/2 =27

Area of Trapezium = 1/2xh(a+b) = 1/2 x 6x(6 + 3) =3 x (9) = 27

Shawon Alam
Jun 18, 2015

6^2-1/2x2x6-1/2x1x6=27

Md Moniruzzaman
Jun 4, 2015

0.5x(sum of parallel arms)x parallel distance

so, 0.5x(6+3)x6=27

Ishan Gulsia
Jun 3, 2015

Just divided it into 3parts*: rectangle and two triangles.. And adding the areas obtained by their respective formulas..

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