Question
How many trailing zeroes (zeroes at the end of the number) does 60! have?
CAT 2021
Correct option is
Explanatory Answer :
We will write the given factorial in the form as 2×5=10 Now, we will consider the factorial in terms of the power of 2.
So, we get 2^5 = 32; 2^6 = 64;
Thus, we get the value of 2^5 is lesser than the given factorial 60! whereas the value of 2^6 is greater than the given factorial 60! .
⇒ So, we get 2^5>2^6
Now, we will consider the factorial in terms of the power of 5.
So, we get 5^2 = 25; 5^3 = 125;
Thus, we get the value of 5^2 is lesser than the given factorial 60! whereas the value of 5^3 is greater than the given factorial 60!
⇒ So, we get 5^2>5^3
Now, we will compare the least powers from 2 and 5.
⇒5^2>2^5 , and we consider the integer with the least power, so we get 5^2 as an integer with the least power.
The number of trailing zeros in the decimal representation of n!
, the factorial of a non negative integer can be determined by this formula: n/5+n/5^2+n/5^3+.....+n/5^k where k must be chosen such that 5^k+1>n
So, we have the value of k
as 2 and thus we get 5^3=125>60
So, writing the powers of 5 in the given factorial 60! , so we get
⇒ Powers of 5
in 60! =[60/5]+[60/5^2]
By simplification, we get
⇒ Powers of 5 in 60!
=[60/5]+[60/2^5]
By dividing the number 5 , we get
⇒ Powers of 5
in 60! =[12]+[2.4]
,Since the powers are greatest integer functions, we get
⇒ Powers of 5 in 60!
=12+2=14
Thus the number of zeros in the given factorial 60! is 14 .
so , A is the correct option