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An infinite geometric series has common ratio 1/8 and sum 80. What is the first term of the series?

 Jan 6, 2021
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We can set a to be the first term and r to be the ratio.

Using the infinite geometric series formula \(S=a/(1-r)\) where S is the sum, we can plug in values to get \(80=a/(7/8)\) so a=70.

:D

 Jan 6, 2021

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