Decimals & Percents · Percent of a number · 6.1

Percent of a number.

To find a percent of a number, turn the percent into a decimal and multiply. 15% of 80 = 0.15 × 80 = 12. “Of” always means multiply.

01 / THE IDEA

See it work.

A percent of a quantity

15% of 80.

12
80

15% × 80 = 12

Watch the method

Find a percent of a number

15% of 80 = 0.15 × 80 = 12.

1 / 2
15% of 8015\%\text{ of }80
1

Turn the percent into a decimal

15% = 0.15.

15%=0.1515\% = 0.15
2

Multiply by the number

“Of” means multiply.

0.15×80=120.15 \times 80 = 12
02 / YOUR TURN

Practice until it feels automatic.

Your turn

Work it out.

Type a decimal, e.g. 0.75.

streak 0
best 0
… =
— / WHY IT WORKS

The idea underneath.

Of = multiply

Convert the percent to a decimal and multiply by the quantity.

Why it works

0.15 of 80 is 12.

03 / WORKED EXAMPLES

From easy to tricky.

EX 1easy

What is 40% of 150?

1

Turn the percent into a decimal

40% = 0.4. 40% = 0.4

2

Multiply by the number

“Of” means multiply. 0.4 × 150 = 60

EX 2medium

What is 40% of 40?

1

Turn the percent into a decimal

40% = 0.4. 40% = 0.4

2

Multiply by the number

“Of” means multiply. 0.4 × 40 = 16

EX 3hard

What is 20% of 90?

1

Turn the percent into a decimal

20% = 0.2. 20% = 0.2

2

Multiply by the number

“Of” means multiply. 0.2 × 90 = 18

04 / COMMON TRAPS

Where students slip.

Trap

Multiplying by 15 instead of 0.15.

Fix

Turn the percent into a decimal first.

Trap

Thinking “of” means add.

Fix

“Of” means multiply.

05 / QUIZ

Test yourself.

The Test

12 problems across three tiers. Auto-graded on submit. Hints and a full walkthrough on every question. Your work is saved on this device — sign in to keep it across devices.

0/12Answered
How to answerType just the value. Formatting won't trip you up — we ignore spaces, capital letters, commas, and subscript style, so t₁ = 5, d = 3 and t1=5,d=3 both count. For a list of numbers, separate them with commas (e.g. 3, 10, 17).
Core

Core (4)

C1

What is 50% of 120?

Need a hint?
  • Make the percent a decimal.
  • Multiply by the number.
C2

What is 75% of 20?

Need a hint?
  • Make the percent a decimal.
  • Multiply by the number.
C3

What is 50% of 30?

Need a hint?
  • Make the percent a decimal.
  • Multiply by the number.
C4

What is 15% of 130?

Need a hint?
  • Make the percent a decimal.
  • Multiply by the number.
Apply

Apply (4)

A1

What is 60% of 60?

Need a hint?
  • Make the percent a decimal.
  • Multiply by the number.
A2

What is 15% of 40?

Need a hint?
  • Make the percent a decimal.
  • Multiply by the number.
A3

What is 25% of 110?

Need a hint?
  • Make the percent a decimal.
  • Multiply by the number.
A4

What is 75% of 100?

Need a hint?
  • Make the percent a decimal.
  • Multiply by the number.
Extension

Extension (4)

E1

What is 10% of 60?

Need a hint?
  • Make the percent a decimal.
  • Multiply by the number.
E2

What is 15% of 190?

Need a hint?
  • Make the percent a decimal.
  • Multiply by the number.
E3

What is 40% of 170?

Need a hint?
  • Make the percent a decimal.
  • Multiply by the number.
E4

What is 10% of 160?

Need a hint?
  • Make the percent a decimal.
  • Multiply by the number.