Question

if the sum of the series 24,20,16...... is 60,then the number of terms is​

Answer 1

a=24

d=a₂-a₁=-4

sₙ=60

n=?

sₙ=n/2(2a+(n-1)d)

60=n/2(2(24)+(n-1)-4)

120=n(48-4n+4)

120=n(52-4n)

30=13n-n²

n²-13n+30

n²-3n-10n+30 (by middle term)

n(n-3)-10(n-3)

(n-10)(n-3)

n=10,3