Lynn's answer to Laraine's Primary 6 Maths Ratio Singapore question.
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At first, the ratio between Siti and Helen was 4:7. However, it became 1:1 when Siti bought 4 more bracelets and Helen sold 5.
By depicting the model, we can see that 4 units + 4 = 7 units - 5
From there, do cross multiplication (actually redundant in this case because ratio is 1:1, but for reference) and solve for 1 unit = 3. Since Siti has 4 units initially, you will get 12
By depicting the model, we can see that 4 units + 4 = 7 units - 5
From there, do cross multiplication (actually redundant in this case because ratio is 1:1, but for reference) and solve for 1 unit = 3. Since Siti has 4 units initially, you will get 12
Date Posted:
4 years ago
How do we know when to apply cross multiplication
Thank you
When the ratio is not 1:1! For eg, if Siti's final number of bracelets is double of Helen's, the ratio would be 2:1.
In this situation, you will need to do cross multiplication, since the amount is no longer equal. Thus 2(7u-5) = 1(4u+4)
Just remember, as long as the ratio is not 1:1, aka they are not equal, you will need to cross multiply
In this situation, you will need to do cross multiplication, since the amount is no longer equal. Thus 2(7u-5) = 1(4u+4)
Just remember, as long as the ratio is not 1:1, aka they are not equal, you will need to cross multiply
Understood, thanks
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