Multiply by 15
Multiply by 10, then add half of that result.
34 × 15 = 510
Fifteen 34s is ten of them plus five of them.
Five 34s is half of ten 34s: 340 ÷ 2 = 170.
Add the parts: 340 + 170 = 510.
Your turn
Three to try in your head — tap what you get.
64 × 15
76 × 15
42 × 15
All 36 shortcuts: the Magic Tricks library.