Kani Math
Cosmic Abacus
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Mixed addition and subtraction drills

Signs that change without warning, so there is no rhythm to settle into and no shortcut to fall back on.

  • 6 rows × 2 digits, add & subtract
  • About 8 min
  • Free, no account

Sample problems

Real problems from this drill, with answers. Nothing to install, no account, no email — work them on paper, on a physical abacus, or in your head.

  1. 1
    22
    + 38
    + 16
    − 38
    − 20
    + 61
    ?
  2. 2
    38
    + 81
    − 96
    + 74
    − 78
    + 66
    ?
  3. 3
    43
    + 19
    − 38
    + 48
    + 17
    + 93
    ?
  4. 4
    85
    + 93
    + 27
    − 31
    − 65
    + 55
    ?
  5. 5
    68
    − 41
    − 20
    + 33
    + 58
    + 68
    ?
  6. 6
    97
    − 39
    + 85
    − 95
    + 32
    − 25
    ?
  7. 7
    99
    + 24
    − 16
    + 43
    + 91
    − 57
    ?
  8. 8
    90
    + 42
    + 72
    − 52
    + 89
    − 60
    ?
  9. 9
    11
    + 26
    + 41
    + 27
    − 44
    + 72
    ?
  10. 10
    83
    + 11
    − 38
    − 14
    + 76
    + 53
    ?
Full answer key
  1. 22 + 38 + 16 − 38 − 20 + 61 = 79
  2. 38 + 81 − 96 + 74 − 78 + 66 = 85
  3. 43 + 19 − 38 + 48 + 17 + 93 = 182
  4. 85 + 93 + 27 − 31 − 65 + 55 = 164
  5. 68 − 41 − 20 + 33 + 58 + 68 = 166
  6. 97 − 39 + 85 − 95 + 32 − 25 = 55
  7. 99 + 24 − 16 + 43 + 91 − 57 = 184
  8. 90 + 42 + 72 − 52 + 89 − 60 = 181
  9. 11 + 26 + 41 + 27 − 44 + 72 = 133
  10. 83 + 11 − 38 − 14 + 76 + 53 = 171

This page is one drill. The app is the whole programme.

Kani Math is a full mental-arithmetic course, not a single exercise. Free to start, no signup, and it runs on the web, Android and iPhone.

  • ✓Nine levels, from the first bead to division
  • ✓Guided lessons that teach the technique, not just drills
  • ✓Flash, listening and abacus drills at a speed you set
  • ✓Versus matches against friends or the computer
  • ✓Say your answers out loud — the app listens and marks them
  • ✓Streaks, coins and badges, with parent and teacher views

Want to stay here? The demo further down runs right on this page.

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Practise it now

The same drill, live in your browser, with a virtual soroban and instant marking.

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Explore the free virtual abacus →How to use an abacus →Mental Math Drill →

About this drill

Pure addition columns and pure subtraction columns both let a learner settle into a groove. Mixed columns remove that. Every row after the first requires reading the sign, choosing the direction, and then choosing between a direct move and a complement — three decisions instead of one, repeated five times with no pattern to anticipate.

This is the drill shape used in most abacus examinations for exactly that reason, and it is the most honest measure of whether a technique is genuinely automatic or merely well-rehearsed in one direction.

How to practise it

  1. 1Read the sign before the number, every single row.
  2. 2Do not scan ahead for an easier ordering — work strictly top to bottom.
  3. 3Keep the same pace on plus rows and minus rows.
  4. 4If you hesitate twice on the same rule, drill that rule on its own page.

Questions

Why is mixed harder than either alone?
Because the decision cost is per row rather than per column. In a pure column you choose the direction once; in a mixed column you choose it five times.
Can the running total hit zero mid-problem?
It can reach zero but never pass below it. The generator guarantees this, matching what a physical soroban can display.
Is this what abacus exams use?
Broadly yes. Most graded abacus examinations use mixed columns because they cannot be passed by drilling one direction.
How do I get faster at these?
Not by hurrying. Isolate whichever rule causes the hesitation, drill it alone until it is silent, then come back to mixed.
Learn the techniqueBig friends (10-complements)Walk through it on the beads →