courses › Mental Arithmetic

Multiply two-digit numbers in your head with friendly shortcuts.

Best in your head · no pen, no calculator why?

Learn first (about 3 minutes)

Opens at level 10.

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Builds on: Times tables (not open yet)

skills · practice stats

From rounds of this course only: box, review and trial answers are left out. Once a skill has 40 tries, it compares your first 20 tries with your last 20.

• Two-digit × one-digit par 7 s not tried yet

  worked example

  34 × 5

  Answer: 170

  1. Split 34 into 30 + 4: 30 × 5 = 150 and 4 × 5 = 20.
  2. 150 + 20 = 170.

• × 5, × 25, × 50 par 7 s not tried yet

  worked example

  50 × 56

  Answer: 2,800

  1. × 50 is × 100 then halve: 56 × 100 = 5,600, and half of that is 2,800.

• Near round numbers par 7 s not tried yet

  worked example

  9 × 19

  Answer: 171

  1. Use 10 × 19 = 190, then remove the one extra copy of 19: 171.

• Double and halve par 7 s not tried yet

  worked example

  50 × 14

  Answer: 700

  1. Halve 14 and double 50: 7 × 100 = 700. The product doesn't change.

rest ladder

Win 3 of your last 4 rounds and the course rests. A win is 90% right, within 2× the round's par. Pass the review when it comes back and the next rest is longer.

1. 1 day
2. 3 days
3. 7 days
4. 14 days
5. 30 days
6. 60 days
7. mastered · every 90 days

your rounds

No rounds yet.