Rule of 101
Just repeat the number — no mental math.
43 × 101 = 4343
101 is 100 + 1: a hundred 43s, then one more 43.
The 43 drops into the two places the zeros left empty: 4343.
So the shortcut: write the number twice. Any 2-digit number works.
Your turn
Three to try in your head — tap what you get.
93 × 101
43 × 101
27 × 101
All 36 shortcuts: the Magic Tricks library.