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primary 5 | Maths
| Area & Volume
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Are my answers to Q4 and Q5 correct? Thanks
Date Posted: 3 years ago
Views: 568
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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
For question 5, correct answer should be
1) find area of the big square 10x10=100cm^2
2) find area of small shaded square 5x5=25cm^2
3) find area of the two shaded triangles
(1/2 x 5 x 10) x 2 = 50cm^2
4) take big square area minus the 3 shaded objects
100 - 50 - 25 = 25cm^2
Your working should not have 1/2 x 10 x 10 because that is the area of a triangle with width and height 10cm, which does not exist. (The shaded triangles have width 5cm, height 10cm)
Hope this helps :)
1) find area of the big square 10x10=100cm^2
2) find area of small shaded square 5x5=25cm^2
3) find area of the two shaded triangles
(1/2 x 5 x 10) x 2 = 50cm^2
4) take big square area minus the 3 shaded objects
100 - 50 - 25 = 25cm^2
Your working should not have 1/2 x 10 x 10 because that is the area of a triangle with width and height 10cm, which does not exist. (The shaded triangles have width 5cm, height 10cm)
Hope this helps :)
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