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(Q). Find the number of trailing zeros in (5²⁰)!.

Solution:- Number of trailing zeros = 

+ +

= 5¹⁹ + 5¹⁸ + 5¹⁷ + ……….. + 5 + 1
now this is a G.P. series & we know that the sum of the G.P. is =

 

here a = 1 = 5⁰& r = = = 5& n = total number of terms in G.P. = 20∴ sum = = Hence total number of trailing zeros = Answer