Decimals & Percents · Multiply decimals · 3.1

Decimal × whole.

To multiply a decimal by a whole number, ignore the point and multiply, then put the point back so the answer has as many decimal places as the decimal you started with. 0.4 × 6 = 2.4.

01 / THE IDEA

See it work.

Watch the method

Decimal × whole

0.4 × 6 = 2.4 (one decimal place).

1 / 2
0.4×60.4 \times 6
1

Multiply ignoring the points

Multiply as whole numbers first.

0.4×60.4 \times 6
2

Count the decimal places

1 + 0 = 1 decimal place(s) in the answer.

=2.4= 2.4
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.

Place the point last

Multiply as whole numbers (4 × 6 = 24), then place the point so the answer has the same number of decimal places as the factors.

Why it works

0.4 × 6 → 24 → 2.4.

03 / WORKED EXAMPLES

From easy to tricky.

EX 1easy

Multiply 0.5 × 2

1

Multiply ignoring the points

Multiply as whole numbers first. 0.5 × 2

2

Count the decimal places

1 + 0 = 1 decimal place(s) in the answer. = 1

EX 2medium

Multiply 0.3 × 2

1

Multiply ignoring the points

Multiply as whole numbers first. 0.3 × 2

2

Count the decimal places

1 + 0 = 1 decimal place(s) in the answer. = 0.6

EX 3hard

Multiply 0.1 × 3

1

Multiply ignoring the points

Multiply as whole numbers first. 0.1 × 3

2

Count the decimal places

1 + 0 = 1 decimal place(s) in the answer. = 0.3

04 / COMMON TRAPS

Where students slip.

Trap

Forgetting to place the point.

Fix

24 must become 2.4.

Trap

Using too many decimal places.

Fix

One decimal in → one decimal out.

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

Multiply 0.9 × 5

Need a hint?
  • Multiply ignoring the point.
  • Give the answer the same decimal places.
C2

Multiply 0.4 × 5

Need a hint?
  • Multiply ignoring the point.
  • Give the answer the same decimal places.
C3

Multiply 0.9 × 4

Need a hint?
  • Multiply ignoring the point.
  • Give the answer the same decimal places.
C4

Multiply 0.2 × 8

Need a hint?
  • Multiply ignoring the point.
  • Give the answer the same decimal places.
Apply

Apply (4)

A1

Multiply 0.7 × 6

Need a hint?
  • Multiply ignoring the point.
  • Give the answer the same decimal places.
A2

Multiply 0.4 × 7

Need a hint?
  • Multiply ignoring the point.
  • Give the answer the same decimal places.
A3

Multiply 0.7 × 9

Need a hint?
  • Multiply ignoring the point.
  • Give the answer the same decimal places.
A4

Multiply 0.6 × 9

Need a hint?
  • Multiply ignoring the point.
  • Give the answer the same decimal places.
Extension

Extension (4)

E1

Multiply 0.2 × 8

Need a hint?
  • Multiply ignoring the point.
  • Give the answer the same decimal places.
E2

Multiply 0.9 × 2

Need a hint?
  • Multiply ignoring the point.
  • Give the answer the same decimal places.
E3

Multiply 0.9 × 5

Need a hint?
  • Multiply ignoring the point.
  • Give the answer the same decimal places.
E4

Multiply 0.1 × 7

Need a hint?
  • Multiply ignoring the point.
  • Give the answer the same decimal places.