Multiply by 101

n × 101

The trick, step by step

1. Multiply by 100: 47 × 100 = 4700.

   47× 1004700

2. Add the number once more: 4700 + 47 = 4747.

   4700+ 474747

3. Longer numbers work the same way: 347 × 101 = 34,700 + 347 = 35,047.

given working answer taken away

Why it works

101 = 100 + 1, so n × 101 = n × 100 + n. For a two digit number the two parts do not overlap, so the digits repeat.