Do you have problems attempting questions on ratios? Throughout my years of tutoring PSLE Maths, I have discovered 5 common scenarios for ratios. I started grouping the problem sums into their respective scenarios and teach my students how to tackle each one. They started to show great improvements in solving problems on ratios.
Hopefully, after reading through this, you will have a better understanding on ratios too.
1. Convert Fraction to Ratio
This is the most fundamental rule in attempting ratios. When we say A is 1/2 of B, it means that the ratio of A : B is 1 : 2. In other words, B has twice of A.
On the other hand, when we say 1/2 of A is equal to 2/3 of B, we need to match their numerators. So we have to change 1/2 to 2/4 so that their numerators are the same. Then the ratio between A : B will be the ratios of their denominators, which is 4 : 3.
2. Transfer from One Side To Another
You are given a ratio A : B. Then, A transfer a part to B and you are given the final ratio. How do you find the beginning amount?
Useful Tip: When A transfer to B, keep in mind that the TOTAL of A and B is the SAME before and after the transfer. This rule will help you to solve this type of questions.
3. Increase/Decrease on Both Sides of Ratios by Same Amount
You are given a ratio A : B. Then A and B increased by the same amount and you are given the final ratio. How do you find their final amount?
Useful tip: Since A and B increase by the same amount, the difference in their ratios must be the SAME before and after the change.
4. Increase/Decrease on Both Sides of Ratios by Different Amount
You are given a ratio A : B. Then A and B increased by the different amount and you are given the final ratio. How do you find their initial amount?
Useful tip: Draw models of A and B for “Before” and “After”. Since they increased by different amounts, usually you need to CUT the model into different parts.
5. Increase on One Side, Decrease on Another Side, by Different Amounts
This is different from scenario 2. Scenario 2 involves transferring from A to B so that the total remains the same. But the total for this scenario will change because both sides change by different amounts. There are a few ways to attempt this type of question, but a useful tip I can offer is the same as scenario 4. You can draw models of A and B for “Before” and “After”, followed by cutting up the models into different parts.
I have compiled 5 common questions for PSLE Ratios to illustrate each scenario. You can view it here.
You can try attempting the questions first. I will be coming up with the videos to show the solutions soon.