To find a percentage, you use a simple idea: “part out of whole, times 100.”

What “percentage” really means

A percentage is just “how much out of 100.”

So 25% means 25 out of 100, 50% means 50 out of 100, and so on.

  • If you know a part (like marks scored, or number of red apples) and a whole (total marks, total apples), you can turn that into a percentage.
  • The core formula is:

Percentage=partwhole×100\text{Percentage}=\frac{\text{part}}{\text{whole}}\times 100Percentage=wholepart​×100

Basic formula with easy examples

General formula

  • Formula: Percentage = (Value ÷ Total value) × 100

Example 1: Test score

You score 45 marks out of 60. What percentage is that?

  1. Part = 45, Whole = 60.
  2. Divide: 45 ÷ 60 = 0.75.
  3. Multiply by 100: 0.75 × 100 = 75%.

So you got 75%.

Example 2: Apples

You have 50 apples and 20 are red.

  1. Part = 20, Whole = 50.
  1. 20 ÷ 50 = 0.4.
  1. 0.4 × 100 = 40.

So 40% of the apples are red.

Example 3: Cats and dogs

There are 40 animals (cats + dogs), and 10 are dogs.

  1. Part = 10, Whole = 40.
  1. 10 ÷ 40 = 0.25.
  1. 0.25 × 100 = 25.

So 25% of the animals are dogs.

Different “percentage” questions

There are three common types of “percentage” problems:

1. Find the percentage (part and whole are known)

Use: Percentage=partwhole×100\text{Percentage}=\frac{\text{part}}{\text{whole}}\times 100Percentage=wholepart​×100.

  • Example: 23 marks out of 50.
    • 23 ÷ 50 = 0.46.
    • 0.46 × 100 = 46%.
      So that’s 46%.

2. Find the part (percentage and whole are known)

Use: Part=Percentage100×Whole\text{Part}=\frac{\text{Percentage}}{100}\times \text{Whole}Part=100Percentage​×Whole.

  • Example: What is 20% of 150?
    • Convert 20% to decimal: 20 ÷ 100 = 0.2.
    • Multiply: 0.2 × 150 = 30.

So 20% of 150 is 30.

You can also think of it as:

  • 10% of 150 = 15, so 20% = 2 × 15 = 30.

3. Find the whole (part and percentage are known)

Use: Whole=Part×100Percentage\text{Whole}=\frac{\text{Part}\times 100}{\text{Percentage}}Whole=PercentagePart×100​.

  • Example: 30 is 20% of what number?
    • Whole = (30 × 100) ÷ 20 = 3000 ÷ 20 = 150.

So the whole is 150.

Percentage increase & decrease

You also often see percentage change problems.

Formula

Percentage change=New value−Old valueOld value×100\text{Percentage change}=\frac{\text{New value}-\text{Old value}}{\text{Old value}}\times 100Percentage change=Old valueNew value−Old value​×100

  • If the result is positive , it’s a percentage increase.
  • If it’s negative , it’s a percentage decrease.

Example: Increase

Price goes from 50 to 65.

  1. Increase = 65 − 50 = 15.
  2. Percentage increase = (15 ÷ 50) × 100 = 0.3 × 100 = 30%.

So the price increased by 30%.

Example: Decrease

Price goes from 80 to 60.

  1. Decrease = 60 − 80 = −20.
  2. Percentage change = (−20 ÷ 80) × 100 = −0.25 × 100 = −25.

So it’s a 25% decrease.

Simple tricks that make it faster

Teachers and math sites suggest a few quick tips to work out percentages more easily, especially in your head.

  • 10% of a number : just move the decimal one place left.
    • 10% of 250 = 25.
  • 5% is half of 10%.
    • 5% of 250 = half of 25 = 12.5.
  • 1% is the number ÷ 100.
    • 1% of 350 = 3.5.
  • Build other percentages from these:
    • 15% = 10% + 5%.
    • 25% = 10% + 10% + 5%.

Example: 15% of 200

  • 10% of 200 = 20.
  • 5% of 200 = 10.
  • Add: 20 + 10 = 30.

So 15% of 200 = 30.

Forum-style quick recap

“How do I find a percentage?” Divide the part by the whole , then multiply by 100. Example: 18 out of 24 18 ÷ 24 = 0.75 0.75 × 100 = 75%

That’s really all “how to find out percentage” means, and the same idea works whether you’re doing marks, prices, or any “part of a whole” scenario.

TL;DR:
Use Percentage=partwhole×100\text{Percentage}=\frac{\text{part}}{\text{whole}}\times 100Percentage=wholepart​×100.

From there, you can also find the part, the whole, or percentage increase/decrease with small rearrangements of the same idea.

Information gathered from public forums or data available on the internet and portrayed here.