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

 Jun 12, 2021

Best Answer 

 #1
avatar+517 
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So it's given that r = 1/8 and S∞ = 80

 

∵ We know that, 

\({S}_{∞} = {a\over 1-r}\)

\(80={a\over 1-{1\over 8}}\)

\(80={8a\over 7}\)

⇒ \(a=70\)

 Jun 12, 2021
 #1
avatar+517 
+2
Best Answer

So it's given that r = 1/8 and S∞ = 80

 

∵ We know that, 

\({S}_{∞} = {a\over 1-r}\)

\(80={a\over 1-{1\over 8}}\)

\(80={8a\over 7}\)

⇒ \(a=70\)

amygdaleon305 Jun 12, 2021

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