Question 122541
A quiz program gives a prize of $5 for the first question answered correctly. The contestant's prize winnings are doubled for each question after the first. How many questions would you need to answer to exceed $1,000,000 in total prize money?
5,10,20,40,80,160....
This is a geometric sequence with r=2 and a=5
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Sum Formula:
S(n) = a[1-r^(n)]/[1-r]
Example: 
S(2) = 5[1-2^(2)]/[1-2] = 5-3/-1 = 15
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Your Problem:
1,000,000 = 5[(2^x)-1]/(2-1)
200,000 = (2^x)-1
200,001 = 2^x
Take the log of both sides to get:
x*log2 = log 200,001
x = [log200,001]/[log2] 
x = 17.6096
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When you answer 18 correctly you will be above 1 million in earnings.
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Cheers,
Stan H.