Arithmetic

Ratio and Proportion

Formula

a : b = c : d (if ad = bc)

What is Ratio and Proportion?

A proportion states that two ratios are equal. If a/b = c/d, then the cross products are equal: a × d = b × c. This is used to solve for unknown values.

Variables

a
a, b — First ratio
c
c, d — Second ratio

Worked Examples

Example 1

If 3 notebooks cost $6, how much do 5 notebooks cost?

Solution:

3/6 = 5/x. Cross multiply: 3x = 30. x = $10

Frequently Asked Questions

Related Formulas

Percentage Change

((New Value − Original Value) / Original Value) × 100

Simple Interest

I = (P × R × T) / 100

Compound Interest

A = P × (1 + R/100)^T

Speed, Distance, Time

Speed = Distance / Time

Ready to Become a Math Champion?

Download the app and compete with players worldwide. Track your progress, climb the leaderboard, and master mathematics.

Download for Android Play in Browser