Question

A geometric series has common ratio \(\frac{1}{3}\). If the sum of first four terms is 200, then the first term is

• A. 90
• B. 100
• C. 115
• D. 145
• E. 135

Hint:

When the common ratio \(r < 1\), it is easier to use \(\frac{a(1-r^n)}{1-r}\). When \(r > 1\), \(\frac{a(r^n-1)}{r-1}\) is often used to avoid negative numbers in the intermediate steps.

Answer 1

Answer: (E)