Question

The first and the last term of an ap are 5 and 45 respectively .If the sum of all its term is 400 find its common difference

Answer 1

a=5

an=45

sn=n/2(a+an)

400=n/2(5+45)

400×2=n×50

800/50=n

16=n

n=16

now,

an=a+(n-1)d

45=5+(16-1)d

45-5=15d

40=15d

40/15=d

d=8/3

common difference is 8/3

hope this answer will help you.