Thursday, 10 December 2015

Q1,P2,J15. How many strings of 5 digits have the property that the sum of digits is is 7.

A)     66           B)330     C)495     D)99.
Answer B.
Explanation.
Let 5 digits ABCDE then their sum is 7.
Let n=7 and r=5.

n+r-1Cr-1=330.
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