Subtract Reversed Numbers
Algebraic shortcut: ab - ba = 9(a-b)
82 − 28 = 54
Split both: 82 is 80 + 2, and 28 is 20 + 8 — the same digits, swapped.
The 8 gains 80 and loses 8: nine 8s. The 2 loses 20 and gains 2: nine 2s off.
So subtract the digits and multiply by 9: 8 − 2 = 6, and 9 × 6 = 54.
Your turn
Three to try in your head — tap what you get.
41 - 14
61 - 16
76 - 67
All 36 shortcuts: the Magic Tricks library.