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1. "A bacteria population doubles in number every 3 hours. If there are 40 individuals now, how many in 24 hours?" SO I used the geometric series sum formula, with n=8(24/3=8), t1=40, and r=2, but I got 10200 as the answer, instead of what the answer key solves as 10240. What did I do wrong?

2. A runner starts jogging 4 kilometres. He increases his distance by 10% each time he runs. a) the distance he runs on the 8th day b) the total distance he has run after 8 days
I have no idea how to do this.

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Bethany
2 answers

  1. you don't need to sum the series. It doubles 8 times in 24 hours, so the population is 40*2^8.

    You'd only need the sum if a new population, double the old one, was added every 3 hours.

    The runner problem is just the same. Every day you multiply the distance by 1.1

    So, on the nth day he runs 4 * 1.1^(n-1)

    The sum is the series where
    a = 40
    r = 1.1
    Sn = 40(1.1^n - 1)/(1.1 - 1)

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    Steve

  2. oh I see, thank you Steve! I did everything except I didn't realize the 1.1 part! I did 0.1 instead haha

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    Wendy

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