1974 AHSME Problems/Problem 21
Problem
In a geometric series of positive terms the difference between the fifth and fourth terms is , and the difference between the second and first terms is . What is the sum of the first five terms of this series?
Solution
Let the first term be and the common ratio be . Therefore, the second term is , the fourth term is , and the fifth term is . We're given that and . Dividing this first equation by this second one, we get . Therefore, , so .
Therefore, the first five terms of this series are , and their sum is .
See Also
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Preceded by Problem 20 |
Followed by Problem 22 | |
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