🧠 MentalMath

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Math topics

Toggle the operations you want to practice and pick a range for each.

Addition +
Subtraction βˆ’
Multiplication Γ—
Division Γ·
Percentages %

Problem presentation

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Practice a fixed number of exercises, or race against the clock β€” you pick the amount.

1 / 20 Score: 0 πŸ”₯ 0
7 Γ— 8

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Mental math techniques

Click a topic to expand it. Practice one technique at a time until it feels automatic.

βž• Addition

1. Work left to right

School teaches right-to-left, but mentally it's easier to add the big parts first.

47 + 38 β†’ 40 + 30 = 70, then 7 + 8 = 15 β†’ 85

2. Round and compensate

Round one number to something easy, then correct at the end.

47 + 38 β†’ 47 + 40 = 87, took 2 extra, so 87 βˆ’ 2 = 85

3. Make a ten (bridging)

Move part of one number to complete a round number.

9 + 6 β†’ take 1 from the 6 to make 10, then 10 + 5 = 15

68 + 27 β†’ take 2 from 27: 70 + 25 = 95

βž– Subtraction

1. Count up instead of down

Subtraction is just the distance between two numbers β€” walk from the small one up to the big one.

83 βˆ’ 47 β†’ from 47 to 50 is 3, from 50 to 83 is 33 β†’ 3 + 33 = 36

2. Round and compensate

Subtract a round number, then give back the difference.

83 βˆ’ 47 β†’ 83 βˆ’ 50 = 33, subtracted 3 too many, so 33 + 3 = 36

3. Work left to right

When no borrowing is needed, subtract tens then ones.

86 βˆ’ 32 β†’ 80 βˆ’ 30 = 50, then 6 βˆ’ 2 = 4 β†’ 54

βœ–οΈ Multiplication

1. Break the number apart (distributive law)

Split one factor into tens and ones, multiply each, add them up. This is the workhorse of mental multiplication.

7 Γ— 46 β†’ 7 Γ— 40 = 280, 7 Γ— 6 = 42 β†’ 280 + 42 = 322

2. Multiply by 5: Γ—10 then halve

48 Γ— 5 β†’ 48 Γ— 10 = 480 β†’ 480 Γ· 2 = 240

3. Multiply by 9: Γ—10 then subtract

9 Γ— 37 β†’ 370 βˆ’ 37 = 333

4. Multiply by 11 (two-digit numbers)

Write the digits apart and put their sum in the middle (carry if needed).

11 Γ— 52 β†’ 5 _ 2 with 5 + 2 = 7 in the middle β†’ 572

11 Γ— 78 β†’ 7 _ 8 with 15 in the middle β†’ 7+1, 5, 8 β†’ 858

5. Double one, halve the other

If one factor is even, you can trade until the problem becomes easy.

16 Γ— 25 β†’ 8 Γ— 50 = 400 β†’ 400

6. Squares ending in 5

Multiply the leading digit(s) by one more than itself and stick "25" on the end.

35Β² β†’ 3 Γ— 4 = 12 β†’ 1225

βž— Division

1. Think of it as a multiplication question

Division is just asking "what times the divisor gives the dividend?" Strong times tables make division automatic.

84 Γ· 7 β†’ 7 Γ— ? = 84 β†’ 7 Γ— 12 = 84 β†’ 12

2. Divide by 4 or 8: halve repeatedly

96 Γ· 4 β†’ half of 96 is 48, half again β†’ 24

3. Divide by 5: double, then Γ·10

245 Γ· 5 β†’ 245 Γ— 2 = 490 β†’ 490 Γ· 10 = 49

4. Break the dividend apart

Split the number into friendly chunks that the divisor goes into cleanly.

96 Γ· 6 β†’ (60 + 36) Γ· 6 β†’ 10 + 6 = 16

312 Γ· 4 β†’ (280 + 32) Γ· 4 β†’ 70 + 8 = 78

οΌ… Percentages

1. Start from 10% β€” just move the decimal

10% of any number is the number with the decimal moved one place left. Build everything else from it.

10% of 340 = 34

30% of 340 β†’ 3 Γ— 34 = 102

2. 5% is half of 10%, 1% moves the decimal twice

5% of 480 β†’ 10% is 48, half β†’ 24

1% of 700 = 7, so 3% of 700 = 21

3. The swap trick: x% of y = y% of x

Percentages commute β€” flip them when the other direction is easier.

8% of 50 = 50% of 8 = 4

4% of 75 = 75% of 4 = 3

4. Know the fraction shortcuts

25% = a quarter (halve twice), 50% = half, 75% = three quarters (quarter Γ— 3), 20% = a fifth (Γ·5).

75% of 84 β†’ 84 Γ· 4 = 21 β†’ 21 Γ— 3 = 63

5. Combine pieces

Split an awkward percent into easy chunks: 10%s, 5%, and 1%s.

23% of 400 β†’ 20% is 80, 3% is 12 β†’ 92

🎧 Tips for listened (voice) mode

Solving problems you only hear trains working memory β€” the core skill of mental math.

  • Visualize the numbers as you hear them β€” picture them written on a whiteboard.
  • Start computing immediately. Process "forty-seven plus…" before the second number even arrives.
  • Repeat without shame. Press R as many times as you need; holding numbers in your head improves quickly.
  • Say intermediate results to yourself ("seventy… eighty-five") to anchor them in memory.