Multiplying multiples of 10

Pre-Algebra Tutorial

Multiplying multiples of 10


A simple trick to multiplying numbers ending in strings of zeroes (multiples of 10)

Sample Problem

Evaluate 250 * 40.

Evaluate 32 * 4000


The zeroes can be ignored until the end of the calculation.
Simply evaluate the product of the operands without the zeroes at the end,
and concatenate them to the answer.

250 * 40 => 25 * 4 = 100 => adding back the two zeroes becomes 10000

32 * 4000 => 32 * 4 = 128 => adding back the 3 zeroes becomes 128000

Note that this trick applies to zeroes at the END of a number. Zeroes that occur inside the the number, e.g 402000 cannot be ignored

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