Multiplying by 101 Trick

Similar to the 11's trick, multiplying by 101 involves adding digits that are separated by a gap. When multiplying a number by 101, you immediately write down the last two digits of the number, then sum the gapped digits to find the preceding digits.

For example, to calculate $438 \times 101$:

• Ones/Tens digits: 38
• Hundreds digit: 4 + 8 = 12 (Write down 2, carry 1)
• Thousands digit: 3 + 1 (carry) = 4
• Ten Thousands digit: 4

The result is 44238.