Revision notes

How to combine two ratios into one

Example

Given that $A : B = 2:3$ and $B : C = 4 : 5$, find the ratio $A : B : C$.

Answer: $ 8 : 12 : 15 $

Solutions

Practice questions

Identify equivalent ratios

1. Which of the following ratios are equivalent to $2 : 5$?

        \text{A}: $4 : 15$

        \text{B}: $10 \text{ cm} : 0.25 \text{ m}$

        \text{C}: $9x : 15x$

        \text{D}: ${a \over 5} : {a \over 2}$

Answer: $ \text{B and D} $

Solutions

Ratio word problems in real-world context

2. A recipe uses flour and sugar in the ratio $5 : 2$. After adding $120$ g of flour, the ratio becomes $4 : 1$. Find the original amount of flour used.

Answer: $ 200 \text{ g} $

Solutions

Using algebra

3. A recipe uses flour and sugar in the ratio $5 : 2$. After adding $100$ g of flour and $100$ g of sugar, the ratio becomes $2 : 1$. Find the final amount of flour used.

Answer: $ 600 \text{ g} $

Solutions

O Level past year questions on ratio

Fully worked, step-by-step solutions to these past-year questions (2016 to 2025) are in the O Level E Maths Solutions page.

Year & paper Comments
2024 P2 Question 2c Word problem in real-world context + Combine two ratios into one
2023 P1 Question 1 Word problem in real-world context
2022 P1 Question 12 Word problem in real-world context (Confusing question!)
2020 P1 Question 12 Word problem in real-world context
2019 P1 Question 19 Word problem in real-world context (need algebra)
2015 P1 Question 12 Word problem in real-world context + Combine two ratios into one
2013 P1 Question 4 Word problem in real-world context
2011 P2 Question 2bi Word problem in real-world context
2010 P1 Question 6 Word problem in real-world context
2009 P2 Question 1a Word problem in real-world context

← Previous topic: Standard form Next topic: Map scales →