Question 745077
the number of terms of an Arithmetic sequence is 15 
so the middle term= (15+1)/2=8th term (+1 for odd no of terms)
so t8=a+(8-1)d=a+7d  (a,d being 1st term & common difference)
the value of it's middle term is 10 
so a+7d=10.........1
the sum of it's terms is S15=(15/2)*(2a+[15-1]d)=7.5*(2a+14d)=7.5*2*(a+7d)
=7.5*2*10=150  putting the value from eqn 1

so the sum =150