Question

Find the sum : $5+(-5)+5+(-5)+...$
i) If the number of terms is 40.
ii) If the number of terms is 45.

Answer 1

Given series is $5+(-5)+5+(-5)+...$

from the series we can observe that for even number of terms the sum is $0$

and for the odd number of terms the sum is $5$

i) if the number of terms is $40$ then the sum is $0$. Since, $40$ is even.

ii) if the number of terms is $45$ then the sum is $5$. Since, $45$ is odd.