Decimals & Percents · Multiply decimals · 3.4

Estimate the point.

Estimating the size tells you where the point goes. 0.6 × 0.5 is about “half of a bit more than a half”, so the answer is around 0.3 — not 3 or 0.03. Estimation catches misplaced points.

01 / THE IDEA

See it work.

Watch the method

Estimate to place the point

0.6 × 0.5 ≈ 0.3, so the point sits right.

1 / 2
0.6×0.50.6 \times 0.5
1

Multiply ignoring the points

Multiply as whole numbers first.

0.6×0.50.6 \times 0.5
2

Count the decimal places

1 + 1 = 2 decimal place(s) in the answer.

=0.3= 0.3
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.

Does the size make sense?

A quick estimate (round the factors) tells you the ballpark, so a misplaced point stands out.

Why it works

0.6 × 0.5 is near 0.3.

03 / WORKED EXAMPLES

From easy to tricky.

EX 1easy

Multiply 0.7 × 0.3

1

Multiply ignoring the points

Multiply as whole numbers first. 0.7 × 0.3

2

Count the decimal places

1 + 1 = 2 decimal place(s) in the answer. = 0.21

EX 2medium

Multiply 0.5 × 0.7

1

Multiply ignoring the points

Multiply as whole numbers first. 0.5 × 0.7

2

Count the decimal places

1 + 1 = 2 decimal place(s) in the answer. = 0.35

EX 3hard

Multiply 0.6 × 0.3

1

Multiply ignoring the points

Multiply as whole numbers first. 0.6 × 0.3

2

Count the decimal places

1 + 1 = 2 decimal place(s) in the answer. = 0.18

04 / COMMON TRAPS

Where students slip.

Trap

Trusting the digits but not the size.

Fix

Estimate to check the point’s place.

Trap

Expecting multiplication to make it bigger.

Fix

Multiplying by less than 1 makes it smaller.

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 0.4 × 0.3

Need a hint?
  • Round the factors to estimate.
  • Place the point near your estimate.
C2

Multiply 0.3 × 0.9

Need a hint?
  • Round the factors to estimate.
  • Place the point near your estimate.
C3

Multiply 0.1 × 0.6

Need a hint?
  • Round the factors to estimate.
  • Place the point near your estimate.
C4

Multiply 0.2 × 0.9

Need a hint?
  • Round the factors to estimate.
  • Place the point near your estimate.
Apply

Apply (4)

A1

Multiply 0.1 × 0.9

Need a hint?
  • Round the factors to estimate.
  • Place the point near your estimate.
A2

Multiply 0.6 × 0.5

Need a hint?
  • Round the factors to estimate.
  • Place the point near your estimate.
A3

Multiply 0.5 × 0.3

Need a hint?
  • Round the factors to estimate.
  • Place the point near your estimate.
A4

Multiply 0.1 × 0.2

Need a hint?
  • Round the factors to estimate.
  • Place the point near your estimate.
Extension

Extension (4)

E1

Multiply 0.3 × 0.2

Need a hint?
  • Round the factors to estimate.
  • Place the point near your estimate.
E2

Multiply 0.5 × 0.2

Need a hint?
  • Round the factors to estimate.
  • Place the point near your estimate.
E3

Multiply 0.9 × 0.2

Need a hint?
  • Round the factors to estimate.
  • Place the point near your estimate.
E4

Multiply 0.3 × 0.2

Need a hint?
  • Round the factors to estimate.
  • Place the point near your estimate.