Question

Find the number of terms required to make the sum equal to zero for the following series 80, 75, 70, ...

Answer 1

Sum =n/2(a+l)

Where n is the no. Of terms, a is the first term and l the last term.

A/Q

n/2[2a +(n-1)d]=0

as l=a+(n-1)d

=>2a+(n-1)d=0

As n cannot be 0

=>2*80+(n-1)(-5)=0

So, (n-1)(5)=160

=>n-1=32

=>n=33(answer)