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Question

Can I cut out the shaded area into a rectangle and triangle to find the shaded area?

Apparently, the solution is to find the area of the large triangle (½ x 12 x 10) and minus the unshaded area (½ x 8 x 6). The answer will be 36 m2

Source: Assesment

Answer

Yes, you can find the same answer as separating the shaded area into a rectangle and a smaller triangle given by 4*6 + 1/2 * 4 * 4 = 24 + 8 = 32 m² if the dotted line is 6 m. But this answer is different from 36 m².

So the only conclusion is the dotted line cannot be 6 m. Logically if the dotted line is 6 m, one of the angle in the triangle must be 45º. But this is impossible if it is an right angle triangle, with sides 12 m and 10 m. So obviously, the answer of 36 m² is wrong. 

I can’t solve this question using psle syllabus. 

If in secondary school, you can use similar triangle to find the length of dotted line = 8 * 10/12 = 6.67 m 

So the area of the shaded area = 4 * 6.67+ 1/2 * (10 – 6.67) * 4 = 33.34 m²

Or

12* 10/2 – 8 * 6.67* 1/2 = 33.32 m²

1 Reply 1 Like ✔Accepted Answer

Yes, the diagram is wrongfully marked.  It doesn’t even say that it is a right-angled triangle 😆 

0 Replies 1 Like

That’s right, just subtract the area of the small triangle from the charge of the large triangle

0 Replies 0 Likes

Publisher MCE replied and will amend error on the next reprint. The book is Math Extra Practice P5.

0 Replies 2 Likes