Decimals & Percents · Add & subtract decimals · 2.1

Add decimals.

To add decimals, line up the decimal points (and the place values), add column by column, and bring the point straight down into the answer.

01 / THE IDEA

See it work.

Watch the method

Add decimals

0.3 + 0.12 = 0.42.

1 / 2
0.3+0.120.3 + 0.12
1

Line up the decimal points

Stack the numbers so the points align, then add column by column.

0.3+0.120.3 + 0.12
2

Bring down the point

The point in the answer lines up too.

=0.42= 0.42
02 / YOUR TURN

Practice until it feels automatic.

Your turn

Work it out.

Type a decimal, e.g. 0.75.

streak 0
best 0
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— / WHY IT WORKS

The idea underneath.

Points in a column

Stack the numbers so the points align; pad with zeros so the columns match; add like whole numbers.

Why it works

0.30 + 0.12 = 0.42.

03 / WORKED EXAMPLES

From easy to tricky.

EX 1easy

Add 1.37 + 0.85

1

Line up the decimal points

Stack the numbers so the points align, then add column by column. 1.37 + 0.85

2

Bring down the point

The point in the answer lines up too. = 2.22

EX 2medium

Add 7.44 + 6.75

1

Line up the decimal points

Stack the numbers so the points align, then add column by column. 7.44 + 6.75

2

Bring down the point

The point in the answer lines up too. = 14.19

EX 3hard

Add 3.75 + 7.17

1

Line up the decimal points

Stack the numbers so the points align, then add column by column. 3.75 + 7.17

2

Bring down the point

The point in the answer lines up too. = 10.92

04 / COMMON TRAPS

Where students slip.

Trap

Lining up the last digits instead of the points.

Fix

Align the decimal points, not the right edges.

Trap

Losing the decimal point in the answer.

Fix

Bring it straight down.

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

Add 9.32 + 6.51

Need a hint?
  • Stack the decimal points.
  • Pad with zeros, then add.
C2

Add 8.77 + 5.14

Need a hint?
  • Stack the decimal points.
  • Pad with zeros, then add.
C3

Add 1.93 + 4.96

Need a hint?
  • Stack the decimal points.
  • Pad with zeros, then add.
C4

Add 6.84 + 1.47

Need a hint?
  • Stack the decimal points.
  • Pad with zeros, then add.
Apply

Apply (4)

A1

Add 7.65 + 2.46

Need a hint?
  • Stack the decimal points.
  • Pad with zeros, then add.
A2

Add 1.95 + 1.25

Need a hint?
  • Stack the decimal points.
  • Pad with zeros, then add.
A3

Add 6.84 + 1.61

Need a hint?
  • Stack the decimal points.
  • Pad with zeros, then add.
A4

Add 8.96 + 7.49

Need a hint?
  • Stack the decimal points.
  • Pad with zeros, then add.
Extension

Extension (4)

E1

Add 0.86 + 5.51

Need a hint?
  • Stack the decimal points.
  • Pad with zeros, then add.
E2

Add 0.31 + 8.68

Need a hint?
  • Stack the decimal points.
  • Pad with zeros, then add.
E3

Add 6.96 + 2.75

Need a hint?
  • Stack the decimal points.
  • Pad with zeros, then add.
E4

Add 1.45 + 2.98

Need a hint?
  • Stack the decimal points.
  • Pad with zeros, then add.