An eight-digit telephone number consists of exactly two zeroes. One of the digits is repeated thrice. Remaining three digits are all distinct. If the first three digits (from left to right) are 987, then find the probability of having only one 9, one 8 and one 7 in the telephone number.	Choose one:
A) 1/18  B) 1/20  C) 1/10  D) 5/47  E) 5/45
Explanation :   Case A: There is only one 9, one 8 and one 7 in the number.   Hence there has to be one digit from {1,2,3,4,5,6} repeated thrice.   Total number of ways in which such a number can exist is :   =&gt;6C1×5!/(3!×2!).   =60.   Case B: One of the three digit {9,8,7} is repeated thrice.   Hence, there will be one digit from {1,2,3,4,5,6}.   Total number of ways in which such a number can exist:   =&gt;3C1×6C1×5!/(3!×2!).   =&gt;540   Total possible telephone numbers:   =60+540= 
<gadget id="calculator">60+540</gadget>
<output>600</output>
600.   Hence the required Probability is 60/600= 1/10.   Answer : 1/10
<result>C</result>
An eight-digit telephone number consists of exactly two zeroes. One of the digits is repeated thrice. Remaining three digits are all distinct. If the first three digits (from left to right) are 987, then find the probability of having only one 9, one 8 and one 7 in the telephone number.