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Product Of Zero

Problem

Take any 2-digit number and multiply the digits together. If this process is continued, all 2-digit numbers will become a single digit number.

For example,75:  7 times 5 = 35, 3 times 5 = 15, 1 times 5 = 5
 68:6 times 8 = 48, 4 times 8 = 32, 3 times 2 = 6
 45:4 times 5 = 20, 2 times 0 = 0

How many 2-digit numbers will finish on zero?

Problem ID: 37 (Mar 2001)     Difficulty: 1 Star

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