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Q.

Number of ways are there to insert + ‘s between the digits of 111111111111111 (fifteen 1’s) so that the result will be a multiple of 30?

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a

1001  

b

2002

c

1002   

d

2000   

answer is D.

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Detailed Solution

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There are fifteen 1’s so the result is always a multiple of 3
Now the number has to be a multiple of 10, so we need to insert 9 plus signs in between the fifteen 1’s, so that the result is a multiple of 10
Required number of ways =  14C9=2002

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