Question

If 5th and 72nd term of an ap are 30and65 respectively what is the sum of the first 20 terms

Answer 1

30=a+(5-1)d 65=a+(72-1)d

30=a+4d 65=a+71d

from the eqution yhe value of a,d will be get

then put it in here

s20=n/2(2a+19d)

ans will be 93676