Given a=310 and n=30.
Let the last term be l and the common difference be d.
The sum of the A.P. is given by S30=230(a+l)=15(310+l).
According to the given condition, S30=l3.
15(310+l)=l3
50+15l=l3
l3−15l−50=0
(l−5)(l2+5l+10)=0
Since l2+5l+10=0 has no real roots, we get l=5.
The last term of the A.P. is l=a+29d.
310+29d=5
29d=5−310=35
d=875
Answer: 875