 ## Question

primary 5 | Maths | Area & Volume

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##### Yew Leong Yeo

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May I know how to solve this question?

Date Posted: 5 months ago
Views: 80
J
5 months ago
Question says both shaded triangles are of equal area. So we make the numerator the same for both fractions since the number of units shaded is the same.

This is the same as saying 2 units out of 7 units are shaded.

We change 1/9 of rectangle to = 2/18 of rectangle. Now the numerators are the same.

This is the same as saying 2 units out of 18 units are shaded.

So we can say :
① Each shaded triangle's area is 2 units
② Area of square is 7 units
③ Area of rectangle is 18 units.

Total area of square and rectangle
= 7 units + 18 units
= 25 units

25 units = 175cm²
1 unit = 175cm² ÷ 25 = 7cm²

Total area of the two shaded triangles
= 2 units + 2 units
= 4 units
= 4 x 7cm²
= 28cm²

Since ¼ of the triangle is shaded,
1 - ¼ = ¾
¾ of the triangle is unshaded.

¾ is just 3 times of ¼.

= 3 x 28cm²
= 84cm²
J
5 months ago

1/9 rectangle = 2/7 □ = 1/8 △
2/18 rectangle = 2/7 □ = 2/16 △

Ratio of area of rectangle : □ : △
= 18 : 7 : 16

Total for rectangle and □ = 25 units

Working is same as above. But you can also find the unshaded triangle area by writing the following :

16 - 2 - 2 = 12
12 x 7cm² = 84cm²
Yew Leong Yeo
5 months ago
Thank you so much.
J
5 months ago
You're most welcome! 