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Mind sports

For the grown-up beside a child who loves mind sports.

The child's own door is Mind sports on Spark & Anvil.

There is no Whetstone tool or course for mind sports yet, so this page is the sideline card and your child's ladder.

The sideline card

Three numbers to notice

  1. On a soroban, each rod has one upper bead worth 5 and four lower beads worth 1, so a rod shows any digit from 0 to 9.
  2. The calendar repeats every 400 years: 146,097 days, exactly 20,871 weeks.
  3. A shuffled deck of 52 cards can come out in about 8 followed by 67 zeros different orders.

On the way home, ask: “Which trick would you like to be able to do in your head?”

Ask because you are curious, and let any answer stand. Print this page for a half-page card.

Numbers checked against: The Soroban / Abacus Handbook; worked by hand, lines 2 and 3 (400 × 365 + 97 leap days = 146,097 = 7 × 20,871; 52! ≈ 8.07 × 10⁶⁷)

Your child's ladder · on Spark & Anvil

The same idea at every age

  1. Ages 3–5Not made yet
  2. Ages 6–8Not made yet
  3. Ages 9–14What Day Was It?
  4. Ages 15–18Fifty-Two Cards in Order

Your child will meet this idea again at every age. The sideline card is the part for you.