Question

How many terms of an AP: 20,19,18......should be taken so that their sum is 300? ​

Answer 1

Answer:

a = 20

d = -1

S = 300

300 = n(2a + (n-1)d )/2

600 = n(40 - n + 1)

600 = n(41-n)

600 = 41n - n^2

n^2 - 41n + 600 = 0

(Solve further using middle term factorisation)

Hope this helps you.