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Que: Find the number of trailing zeroes after the rightmost non-zero digit in the value of 55!?

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by Max@Math Revolution » Wed Aug 11, 2021 9:04 pm

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Que: Find the number of trailing zeroes after the rightmost non-zero digit in the value of 55!?

A) 3
B) 5
C) 7
D) 11
E) 13
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Re: Que: Find the number of trailing zeroes after the rightmost non-zero digit in the value of 55!?

by Max@Math Revolution » Thu Aug 12, 2021 8:59 pm
Solution: 55! = 55 * 54 * 53 *………. * 3 * 2 * 1

=> When ‘5’ is multiplied by an even number, it results in ‘0’.

=> Numbers in 55! , which has ‘5’ as the factor are: 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55

=> 25 and 50 will have ‘2’ (5’s). Hence, we have 13 ‘5’s’ and at least 13 even numbers in 55! , which when multiplied by 5 will result in ‘0’.

E is the correct answer.

Answer E.
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