Wenna Lee's answer to Ashlyn's Primary 4 Maths Singapore question.
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Hope this helps :)
Date Posted:
4 years ago
hey..can you make it clearer? im having difficulty finding out af and ed
AF and ED total length is BC. Is like how to label AB. AB is CD+EF.
can you tell me the length? i tried dividing by 2 but it cant so any more clues?
The question do not need you to divide the lines. The idea here is how you are able to see that both lines add up to be BC.
AOne way is to find the lengths AF and ED but do note that this is not the recommended approach.
Ashlyn, you will need to be able to “shift” lengths around as you find the perimeter of such shapes. This is an important approach as the lengths of the short lines are sometimes not provided.
In other words, you will need to shift line ED leftwards such that it is joined below AF. Similarly, FE needs to be shifted downwards such that it is joined to the left of DC. The new shape looks like a rectangle. Since we are shifting lengths and not adding new lengths, there is no change in values of perimeters. So the perimeter of that figure is the same as the perimeter of the new rectangle.
Note, however, that the shifting of lengths applies only to perimeters. Do not do so to find the area of the figure.
Ashlyn, you will need to be able to “shift” lengths around as you find the perimeter of such shapes. This is an important approach as the lengths of the short lines are sometimes not provided.
In other words, you will need to shift line ED leftwards such that it is joined below AF. Similarly, FE needs to be shifted downwards such that it is joined to the left of DC. The new shape looks like a rectangle. Since we are shifting lengths and not adding new lengths, there is no change in values of perimeters. So the perimeter of that figure is the same as the perimeter of the new rectangle.
Note, however, that the shifting of lengths applies only to perimeters. Do not do so to find the area of the figure.