Answer:
since a,7,b,23,c are in A.P.
first term t1=a
second term t2=7
common difference (d)=7-a
forth term t4=a+3d
23=a+3(7-a)
23=a+21-3a
23=21-2a
2a=21-23
a=-2/2=-1
common difference =7-a=7--1=8
third term =a+2d=-1+2×8=15
:.b=15
5th term =c
a+4d=c
c=-1+4×8=31
a=-1
b=15
c=31
