The sum ∑i=0m 10i20m−i, where ,pq=0, if p<q is maximum, when m is
5
10
15
20
∵∑i=0m 10i20m−i=∑i=0m 10Ci20Cm−1
= Coefficient of xm in the expansion of (1+x)10(1+x)20=30Cm
It is maximum, when
m=302=15