The Open Hand · ages 9-14

1089

The idea: why reverse-and-subtract always lands on 1089.

Danya points at a chalkboard beside a painted wagon at dusk while Beto, Nabo and Marlow watch.

Read it

Who is in this book

Nabo Reverse, subtract, reverse, add, and you always land on 1089 from ShowMath
Marlow Rehearse, perform, then reveal the reason instead of protecting the mystery from ShowMath
Danya a child of the Green Asks "how do we know?"
Elvi There is always room in the middle; keep every place, even a zero from ShowMath
Beto a child of the Green Takes things apart

Every recurring character has a short tune, so you can tell who is on stage before a word is said. The tunes play only when you tap, and the Reading Access sound switch turns them off.

The Honest Page

Which parts of this story are true, stretched or made up?

True

Take any three-digit number whose first and last digits are different, reverse it, subtract the smaller from the bigger, then add that answer to its own reverse. You always get 1089, as long as you keep three places (099, not 99).
Most books state the trick with a stricter rule, first and last digits that differ by more than 1, so nobody meets the 099 case. Keep three places and the smaller gap works too. Source
The difference is always 99 times the gap between the first and last digits, so it is always a multiple of 99.

Stretched

Danya spots the whole pattern in one evening. What we simplified: Most people need many tries, a list and some help noticing the 9 in the middle; the book squeezes that into one night.

Made up

The Open Hand troupe, the painted wagon and the trunk with seven locks are made up. Nabo, Elvi and Marlow come from ShowMath.

Tell it back

Tell the story in your own words: who was there, what went wrong, and what they found out. Then the first of seven locks on the troupe's trunk, which opens after the Reveal goes on your belt.

Ring the hammer for someone

Pick this book for someone younger. The link carries only the book, and it will wait for them on the Green.

Across the Table → For the grown-up: the story in three lines, one question to ask, and one thing to do together.