Mental Math · Addition · A2

Add in chunks.

Another way to add: keep one number whole and add the other one chunk at a time — first its tens, then its ones. You only ever track one running total, which is easy to hold in your head.

01 / THE METHOD

How to think about it.

Watch the method

Add in friendly chunks

Hold 145 in mind and feed in 38 piece by piece: +30 gets you to 175, then +8 gets you to 183. One number stays still while the other arrives in easy bites.

1 / 2
145+38145 + 38 = ?
1
145+30=175145 + 30 = 175

Add the tens of 38.

2
175+8=183175 + 8 = 183

Add the ones of 38.

02 / YOUR TURN

Practice until it feels easy.

Your turn

Solve it in your head.

Use the method, then check. Stuck? Reveal the steps.

streak 0
best 0
… =
— / WHY IT WORKS

The idea underneath.

One running total

Instead of juggling several partial sums, you grow a single number. 145 → (+30) → 175 → (+8) → 183. Your mind only ever holds one value.

Why it works

Like climbing stairs: each chunk is one step up to the next landing.

03 / WORKED EXAMPLES

From easy to tricky.

EX 1easy

67 + 25

1

Add the tens

67 + 20 = 87.

2

Add the ones

87 + 5 = 92.

EX 2medium

145 + 38

1

Add the tens

145 + 30 = 175.

2

Add the ones

175 + 8 = 183.

EX 3hard

472 + 58

1

Add the tens

472 + 50 = 522.

2

Add the ones

522 + 8 = 530.

04 / COMMON TRAPS

Where students slip.

Trap

Adding the ones before the tens.

Fix

Add the tens chunk first. It lands you near a round number and keeps the ones step tiny and safe.

Trap

Losing track of the running total mid-way.

Fix

Say each landing out loud or in your head: 175 … 183. Lock in the chunk before adding the next.

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

145 + 38 = ?

Need a hint?
  • Keep the first number whole; add the second in chunks.
  • Add the tens chunk first, then the ones.
C2

67 + 25 = ?

Need a hint?
  • Keep the first number whole; add the second in chunks.
  • Add the tens chunk first, then the ones.
C3

234 + 45 = ?

Need a hint?
  • Keep the first number whole; add the second in chunks.
  • Add the tens chunk first, then the ones.
C4

58 + 36 = ?

Need a hint?
  • Keep the first number whole; add the second in chunks.
  • Add the tens chunk first, then the ones.
Apply

Apply (4)

A1

326 + 47 = ?

Need a hint?
  • Keep the first number whole; add the second in chunks.
  • Add the tens chunk first, then the ones.
A2

472 + 58 = ?

Need a hint?
  • Keep the first number whole; add the second in chunks.
  • Add the tens chunk first, then the ones.
A3

153 + 86 = ?

Need a hint?
  • Keep the first number whole; add the second in chunks.
  • Add the tens chunk first, then the ones.
A4

245 + 67 = ?

Need a hint?
  • Keep the first number whole; add the second in chunks.
  • Add the tens chunk first, then the ones.
Extension

Extension (4)

E1

367 + 255 = ?

Need a hint?
  • Keep the first number whole; add the second in chunks.
  • Add the tens chunk first, then the ones.
E2

488 + 125 = ?

Need a hint?
  • Keep the first number whole; add the second in chunks.
  • Add the tens chunk first, then the ones.
E3

639 + 184 = ?

Need a hint?
  • Keep the first number whole; add the second in chunks.
  • Add the tens chunk first, then the ones.
E4

754 + 167 = ?

Need a hint?
  • Keep the first number whole; add the second in chunks.
  • Add the tens chunk first, then the ones.