Add & Subtract Decimals Practice
Line up the points, pad the zeros, compute — then check every answer against an estimate.
How to enter answers
- Decimals: type
3.65(trailing zeros optional). - Estimates: type the whole number, e.g.
8. - Always line up the decimal points on paper first.
Problem types
Add decimals
Line up the points, add the columns.
Example: 2.45 + 1.2 = 3.65
Subtract decimals
Pad, borrow, compute.
Example: 5.2 − 1.35 = 3.85
Tenths pairs
Tenths that complete a whole.
Example: 0.3 + 0.7 = 1
Count the places
How many digits after the point?
Example: 3.65 has 2
Missing addend
Work backwards from the total.
Example: ? + 0.34 = 1.2 → 0.86
Estimate the sum
Round first, add second.
Example: 4.87 + 2.95 ≈ 8
Common slip-ups
Lining up the right edge
2.45 + 1.2 = 14.45 lines up the wrong edge. Line up the points: 3.65.
Forgetting to pad
5.2 − 1.35 needs 5.20 — pad so every column has a digit.
No estimate, no safety net
A slipped point turns 78.2 into 7.82. Estimate first.