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ohaa [14]
2 years ago
15

If 2 + 2^2 + 2^3 +...+ 2^n = 510 then n = ?

Mathematics
2 answers:
jonny [76]2 years ago
5 0

Answer:

N= 8

Step-by-step explanation:

Bumek [7]2 years ago
3 0

Answer:

n = 8

Step-by-step explanation:

This Geometric series. r = 2 and a = 2

S_{n}= \dfrac{a(r^{n}-1)}{r-1}\\\\\\\dfrac{2(2^{n}-1)}{2-1}=510\\\\\dfrac{2*(2^{n}-1)}{1}=510\\\\2*(2^{n}-1) = 510\\\\2^{n-1}=\dfrac{510}{2}\\\\2^{n} - 1 = 255\\\\2^{n}=255+1\\\\2^{n} = 256\\\\2^{n} =2^{8}

n = 8

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Remark

The answer to this problem is less than the smallest time of the two people working together. that fact lets out C and D (38 minutes and 75 minutes). Now you have to choose 15 minutes and 18 minutes. There's a method. No guessing needed.

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Answer working together it took them 18 minutes  <<<<< 
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