Consider the following series: 50 + -10 + 2 + ... what is the sum of the first 5 terms?

1 Answer
Apr 25, 2018

1024/25 or 41.68

Explanation:

This series looks like a geometric progression(GP) with a common ratio of -1/5. A geometric progression is a series of the form a,a*r,a*r^2,... where ‘r’ is called the common ratio.The formula for the sum of a geometric series is a*(r^n-1)/(r-1) where ‘a’ is the first term, ‘r’ is the common ratio and ‘n’ is the number of terms. Substituting the values from the given series, we get 50*(((-1/5)^5)-1)/((-1/5)-1

This simplifies into 1024/ 25 or 41.68