Mental Math · Decimals · Multiply
To multiply decimals, forget the points and multiply the digits as whole numbers. Then count how many decimal places were in the question, and put that many back in the answer.
Watch the method
1.2 × 3: ignore the point → 12 × 3 = 36. The question has one decimal place, so the answer does too: 3.6.
Ignore the decimal point and multiply.
One decimal place in the question → one in the answer.
Your turn
Use the method, then check. Stuck? Reveal the steps.
Each decimal place is a division by ten hidden in the number. Multiply the plain digits, then restore one place for every decimal place in the question. 0.3 × 0.4 has two places: 12 → 0.12.
Why it works
Tenths times tenths makes hundredths — two places.
2.4 × 2
Ignore point
24 × 2 = 48.
Place it
One place → 4.8.
0.3 × 0.4
Ignore points
3 × 4 = 12.
Place it
Two places → 0.12.
1.3 × 2.4
Ignore points
13 × 24 = 312.
Place it
Two places → 3.12.
Lining up the points like in addition.
For multiplying you don't line up points — you multiply the digits and COUNT places afterward.
Using too few decimal places.
0.3 × 0.4 = 0.12 (two places), not 1.2. Count places from BOTH numbers.
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.
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).1.2 × 3 = ?
2.4 × 2 = ?
0.5 × 6 = ?
3.1 × 4 = ?
0.3 × 0.4 = ?
1.5 × 0.2 = ?
2.5 × 1.2 = ?
0.7 × 0.8 = ?
1.3 × 2.4 = ?
4.5 × 1.2 = ?
0.25 × 4 = ?
6.2 × 0.5 = ?