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# Series

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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

#1
+524
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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
+524
+2

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