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smc

number theory senior

Problem

Let equal the product of 3,659,893,456,789,325,678 and 342,973,489,379,256. The number of digits in is:
(A)
(B)
(C)
(D)
Solution
Through inspection, we see that the two digit number digits. Notice that any number that has the form multiplied by another will have its number of digits equal to the sum of the original numbers' digits. In this case, we see that the first number has digits, and the second number has digits. Note: this applies for numbers Hence, the answer is digits
Final answer
C