Percentage is a chapter in PSLE Maths which is very closely related to Fractions and Ratios. You need to know how to convert percentage to fractions, fractions to ratios, and vice versa. You also must be clear on how to find percentage increase and percentage decrease of a number.
Here are 5 common types of percentage problem sums in PSLE Maths.
1. Convert Percentage to Fractions or Ratios
When we want to convert percentage to fractions, we simply divide the percentage by 100. So 20% = 20/100 = 1/5. So when we say A is 20% of B, it means A is 1/5 of B. So the ratio of A : B is 1 : 5.
On the other hand, when we say A is 20% more than B, what do we do? Similarly, we convert 20% to 1/5. So A is 1/5 more than B. In this case, B has 5 units and A has 1 more unit than B. So the ratio of A : B is 6 : 5.
John has 50% as much money as Tom. Tom has 80% as much as Ron. How many more percent of money does Ron have than John?
2. Finding Percentage Increase/Decrease
How do you find percentage increase when a number increases?
Useful tip: You always let the original number be 100%. Then percentage increase = Increase/Original * 100%.
Similarly, when a number increases by a certain percent, how do you find the final number?
Useful tip: You always let the original number be 100%. Then you add up 100% by the percentage increase and multiply the answer with the original number.
For example, A is 50 at first. After increasing by 20%, the final number is 120% multiply by 50 which is 60.
Peter bought a computer for $800. This was 20% less than the usual price.
a)If he sold it at 5% more than the selling price, how much did he sell the computer for?
b) If he sold it at 5% more than the usual price, how much did he sell the computer for?
3. GST, Discount, Interest
Always let the original amount be 100%. GST and Interest is added to the original amount. Discount is deducted from the original amount.
Question: Susan is selling her blouse for $50. One day, she decided to raise the price by 10%. However, her customer felt that the price was too steep so she decided to give a discount of 5%.
a. How much is the blouse now?
b. If there is additional 7% GST, how much will the blouse cost now?
4. Using Ratios
Sometimes, it is useful to use ratios to solve percentage problem sums. It is because ratios allow us to find the difference of the units easily.
Question: 80% of the passengers on the train were adults. 152 more passengers boarded the train. As a result, the number of adults increased by 10% and the number of children increased by 150%. How many passengers are there on the train now?
Useful tip: Find the beginning ratio of Adults : Children. Then, apply the percentage change to find the final ratio.
5. Using Models
Question: Tank A contained twice as much water as Tank B. When 10% of the water from A and 10% of the water from B were transferred to Tank C, Tank C will have 72L of water, which was 20% more than before. How many litres of water were there in Tank A at first?
Useful tip: Draw the starting model of Tank A and B. Then cut the model and transfer the units to Tank C.
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