Question

How many terms of the series 30+27+24+.....must be taken do that the sum may be 156

Answer 1

First term (a) = 30

Common Difference(d) = -3

Sum of first n terms = 156

Let no. of terms be n

We know that,

Sn=n/2(2a+nd-d)

156=n/2(60-3n+3)

156=n/2(63-3n)

312=63n-3n^2

3n^2-63n+312=0