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Cosmic Abacus
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Mental math test for adults

Twelve problems sized for adult brains — three digits, five rows, no mercy. Take it cold, note your time, and see what a few weeks of practice does to it.

  • 5 rows × 3 digits, add & subtract
  • About 5 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
    825
    − 332
    + 192
    − 490
    + 678
    ?
  2. 2
    452
    + 121
    − 116
    + 812
    + 398
    ?
  3. 3
    489
    + 154
    − 345
    + 995
    + 515
    ?
  4. 4
    398
    + 948
    + 433
    − 202
    − 284
    ?
  5. 5
    769
    − 316
    + 472
    + 660
    + 312
    ?
  6. 6
    421
    − 275
    + 775
    + 921
    + 698
    ?
  7. 7
    349
    + 936
    − 767
    − 362
    + 859
    ?
  8. 8
    928
    + 376
    + 473
    + 146
    − 549
    ?
  9. 9
    339
    + 325
    + 565
    − 497
    + 762
    ?
  10. 10
    224
    + 776
    + 777
    − 897
    + 791
    ?
  11. 11
    711
    + 405
    − 372
    + 630
    − 168
    ?
  12. 12
    566
    + 882
    − 356
    + 857
    + 179
    ?
Full answer key
  1. 825 − 332 + 192 − 490 + 678 = 873
  2. 452 + 121 − 116 + 812 + 398 = 1667
  3. 489 + 154 − 345 + 995 + 515 = 1808
  4. 398 + 948 + 433 − 202 − 284 = 1293
  5. 769 − 316 + 472 + 660 + 312 = 1897
  6. 421 − 275 + 775 + 921 + 698 = 2540
  7. 349 + 936 − 767 − 362 + 859 = 1015
  8. 928 + 376 + 473 + 146 − 549 = 1374
  9. 339 + 325 + 565 − 497 + 762 = 1494
  10. 224 + 776 + 777 − 897 + 791 = 1671
  11. 711 + 405 − 372 + 630 − 168 = 1206
  12. 566 + 882 − 356 + 857 + 179 = 2128

Practise it now

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

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About this drill

Most mental math tests online are written for eight-year-olds, which tells you nothing except that you are not eight. This one starts where adult comfort ends: five rows of three-digit numbers, mixed addition and subtraction, against the clock.

There is no trick to passing it. Working memory holds the running total while your eyes take the next row — exactly the skill abacus students train until it stops feeling like effort. If the test humbles you, that is the point of a benchmark: it gives practice something measurable to move.

How to practise it

  1. 1Press start and the first problem appears — rows flash one after another.
  2. 2Add and subtract as the rows come, holding the running total in your head.
  3. 3Type the answer when the last row has shown, then move to the next problem.
  4. 4Finish all twelve and note your score and total time — that pair is your baseline.

Questions

Is this test suitable for adults with no abacus background?
Yes — it assumes nothing except ordinary arithmetic. The abacus connection is on the training side: mental soroban is one proven way to make this kind of running calculation fast, and adults can learn it too.
What is a good score?
Cold, most adults miss several and take well over a minute per problem. Weekly repeats matter more than the first number — the difficulty never changes, so improvement is real, not easier questions.
Can adults actually improve mental math, or is it fixed?
It improves with practice at any age. Adult learners on the soroban ladder routinely reach levels they assumed were for children — the blog post on adults learning the soroban covers what to expect.