Question

Find the 31 term of ap whose 11 term is 38 and 16 term is 78

Answer 1

a11=38
a+10d=38.........(1)
a16=78
a+15d=78...........(2)
subtracting second from 1
-5 d=-40
d=8
substituting the value of d in equation 1
a+10×8=38
a=-58
a31=a+(31-1)×d
=-58+30×8
= -58+240
=182