The sum to infinity of a geometric progression is 5 and the sum to infinity of another series formed by taking the first, fourth, seventh, tenth, ... terms (that is, U1+U4+U7+U10+...) is 4. Find the common ratio of the first series.

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- May 8th 2011, 12:01 AMPunchSum to infinity
The sum to infinity of a geometric progression is 5 and the sum to infinity of another series formed by taking the first, fourth, seventh, tenth, ... terms (that is, U1+U4+U7+U10+...) is 4. Find the common ratio of the first series.

- May 8th 2011, 12:11 AMFernandoRevilla
__Hint__

The ratio of the second series is the cube of the first one. - May 8th 2011, 12:28 AMPunch
- May 8th 2011, 12:40 AMmr fantastic