# 4 must know concepts for PSLE ratio

When having an exam, you don’t want to mess up with the marks that come with PSLE ratio word problems. These marks are a chunk of the total marks for the exam, and it’s only safe to earn as much as you can.

Various methods are involved in solving PSLE math’s, and any one of those methods can be used by the math’s tutor to trick you. However, irrespective of how the questions might be twisted, there are 4 basic PSLE ratio that will be tested during an exam, and these are;

**Example:
**John and Peter both have shares in a particular sum of money, in the ratio
5:6. After a couple of days, Peter spent $16, this caused the ratio to become
3:2. At the end, how much does Peter have?

**The “Constant part”:**This simply means that in a Mathematics question, one of the various parts didn’t change, while others did. This is a basic mathematical word problem with a simple approach to solving it. In solving this forms of math problem, all that needs to be done is to make the part that refused to change, equal to each other. If you see a question in the format below from your math tutor, this is the simple approach needed to solve it.

In solving this, you should know that the amount owned by John would remain the same in both cases, as he did not spend any amount of his share.

**The “Constant Total”:**This refers to a case in which the total of a word problem remained the same. Most times, this concept is used when dealing with ‘internal transfer’. Taking a look at this scenario: If X transfers some cash to Y, the amount of cash on X would reduce, while that of Y would get to increase, and by the same amount. However, the total amount of cash on both persons would remain the same, before and after the transfer.

**Example:**
John and Peter both have shares in a particular sum of money, in the ratio 5:4.
After a couple of days, John gave Peter about $20, this caused them to have the
same amount of money. At the end, how much money does Peter have in the end?

In solving this, you should know that the total amount of money owned by the two persons would remain the same.

**The “Constant difference”:**This refers to the case in which the difference remained the same. In most cases and examinations, you would find out that this concept is used with respect to” Age”.

Irrespective of the number of years that goes by, the difference in the ages of two individuals will always remain the same. This is simply because both individuals grow older, together.

**Example:
**John and Peter both have ages that are in the ratio 4:7. However, in 3
years’ time, they would be at ages with the ratio 3:5. What is the current age
of Peter?

In solving this, you should put into consideration that the both John and Peter grow older, together. Hence, the difference in their ages would always remain the same.

**The “Everything Changed”:**This is just as the name implies, in questions like this, every variable is bound to change. The difference changed and so also did the total. None of the variables remained the same.

In most exams, questions that run on this principle would most likely carry the last 5 marks. This is a very important type of question, and you should ensure that you maximize it. However, there are a number of methods that can be used to solve these types of problems. The breakdown of a method goes thus,

**Example:**
The ratio of John’s money to Peter’s was 2:1. Soon, John saved another $60,
while Peter spent $150. This caused the ratio to change to 4:1. What was the
amount of money John had in the first place?

In solving this, these steps are applicable:

- Pen down the starting ratio, then effect the changes
- Have a comparison between the final units and the final ratio
- Have a cross multiplication of the final units and the final ratio
- Finally, solve for just one unit.

These four concepts are the very basics and can be used in examining you, once you understand them, you are good to go. **A**

Categorised as: G Post

Thank you! This is exactly what I needed to create this kind of problem in our primary school mathematics game that we are building. I particularly like the ratio problems, and have thought of some ways to include this kind of challenge in our game. Thanks again, eternally grateful!