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2. If in the expansion of (1+x)15, the coefficients of (2r +3)th and (r-1)th terms are equal, then the value of r is:

6. What is the coefficient of x5 in the expansion of (1-x)-6?

12. In a binomial expansion with power 13,

14. In the expansion of (a+b)n , n N the number of terms is:

15. The number of terms in the expansion of (x - y + 2z)7 are:

18. If in the expansion of (1+x)20, the coefficients of rth and (r+4)th terms are equal, then the value of r is equal to: