You can multiply any two digit-number by 101 in one second or maybe less using this amazing multiplication trick.
Let ab represent the number you would like to multiply by 101.
Then, ab × 101 = abab
Examples
64 × 101 = 6464
12 × 101 = 1212
10 × 101 = 1010
99 × 101 = 9999
51 × 101 = 5151
37 × 101 = 3737