Teo Jer Rei's answer to Catherine Wee Mui Chin's Primary 5 Maths Area & Volume Singapore question.
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Hi, Qn4 has an error. The area of the square is actually 4x4 =16. This is because the question stated “square of sides 4cm”
Area of cut out square 4x4=16 cm^2
Area of the big triangle should be
1/2 x (4+3) x (4+4+4) = 42cm^2
Then take the big triangle minus the area of the square that was cut out
42cm^2 - 16cm^2 = 26cm^2 (ANS)
your method to find the area of each of the small triangles won’t work, because the 3 triangles do not have equal dimensions. The top most triangle does not have a base of 4cm, it is slightly longer than the square
Area of cut out square 4x4=16 cm^2
Area of the big triangle should be
1/2 x (4+3) x (4+4+4) = 42cm^2
Then take the big triangle minus the area of the square that was cut out
42cm^2 - 16cm^2 = 26cm^2 (ANS)
your method to find the area of each of the small triangles won’t work, because the 3 triangles do not have equal dimensions. The top most triangle does not have a base of 4cm, it is slightly longer than the square
Date Posted:
3 years ago
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