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Que: Find the number of trailing zeroes after the rightmost non-zero digit in the value of 30!

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Que: Find the number of trailing zeroes after the rightmost non-zero digit in the value of 30!

by Max@Math Revolution » Mon Jul 12, 2021 10:30 pm

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Que: Find the number of trailing zeroes after the rightmost non-zero digit in the value of 30!

A) 3
B) 6
C) 7
D) 10
E) 25
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Re: Que: Find the number of trailing zeroes after the rightmost non-zero digit in the value of 30!

by Max@Math Revolution » Tue Jul 13, 2021 8:47 pm
Solution: 30! = 30 * 29 * 28 *………. * 3 * 2 * 1

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

Numbers in 30! , which has ‘5’ as the factor are: 5, 10, 15, 20, 25, 30

25 will have ‘2’ (5’s). Hence, we have 7 ‘5’s’ and at least 7 even numbers in 30! , which when multiplied by 5 will result in ‘0’.

C is the correct answer.

Answer C.
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