5 Percent of Any Number in 4 Seconds

You can find 5 percent of any number in 4 seconds using this trick. So what is the trick?

In this lesson, you will learn

  • A two-step trick to find 5% of any number in your head
  • Why dividing by 2 and moving the decimal point gives 5%
  • How to use the trick with even numbers, odd numbers and money

The Trick: Divide by 2, Then Move the Decimal Point

Rule

Trick: Divide the number by 2 and move the decimal point one place to the left.

The process just involves two easy steps as shown in the following examples.

Remember

Why it works: moving the decimal point one place to the left divides a number by 10, which gives 10%. 5% is half of 10%, so you also divide by 2.

What is 5% of 40?

Show answer

2. 40 ÷ 2 = 20 = 20.0, and moving the decimal point one place to the left gives 2.00 = 2.

Four Examples of Finding 5% of a Number

Example #1: 5% of 180
  1. Divide 180 by 2: 1802 = 90 = 90.0
  2. Move the decimal point one place to the left: 9.00

5% of 180 = 9

Example #2: 5% of 13
  1. Divide 13 by 2: 132 = 6.5
  2. Move the decimal point one place to the left: 0.65

5% of 13 = 0.65

Common mistake

Skipping step 1. Moving the decimal point alone gives 10% of the number, not 5%: for 13 that is 1.3, which is twice too big.

Example #3: 5% of 650
  1. Divide 650 by 2: 6502 = 325 = 325.0
  2. Move the decimal point one place to the left: 32.50

5% of 650 = 32.5

Example #4: 5% of 36
  1. Divide 36 by 2: 362 = 18 = 18.0
  2. Move the decimal point one place to the left: 1.8

5% of 36 = 1.8

5% of 36: step 1 divides 36 by 2 to get 18.0, and step 2 moves the decimal point one place to the left to get 1.8

What is 5% of 70?

Show answer

3.5. 70 ÷ 2 = 35 = 35.0, and moving the decimal point one place to the left gives 3.50 = 3.5.

Summary

  • To find 5% of a number, divide the number by 2.
  • Then move the decimal point one place to the left.
  • The trick works because 5% is half of 10%, and moving the decimal point one place to the left gives 10%.
  • For an odd number, the result of step 1 ends in .5, for example 13 ÷ 2 = 6.5, so 5% of 13 = 0.65.

Test Yourself: 10-Question Quiz

Now check what you learned. Every answer is explained, and each time you play you get new questions.

Question 1 of 10Score: 0

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