<PRE><B>Question 745077</B>

The nth term of an AP is given by the formula Tn = a+(n-1)d

t15 = a+14d

The middle term is the 8th term

T8=a+7d

10=a+7d
multiply by 2

20=2(a+7d)
20=2a+14d


Sum of n terms = Sn = n/2[2a+(n-1)d]

s15 = 15/2[2a+(15-1)d]

S15= 15/2[2a+14d]

but 2a+14d=20

S15=15/2( 20)

S15=150

sum of 15 terms = 150</PRE>