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28 July, 19:30

Five children know a secret. Every day, the number of children who know the secret doubles. There are 1,280 children in the school. Of the secret continues to spread at this rate, how long will it take until all of the children in the school know the secret?

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Answers (2)
  1. 28 July, 20:37
    0
    9 days

    Step-by-step explanation:

    Since the secret spread at a geometric rate we will use the geometric progression formulae

    ar^n-1

    First term = a = 5

    common ratio is 2

    For the nth term

    5*2^n-1 = 1280 divide both sides of the equation with 5

    2^n-1 = 256

    2^n-1 = 2^8

    n-1 = 8

    n = 8+1

    n=9

    All the children will know the secret in 9 days

    Alternatively

    2nd day = 5*2^2-1

    5*2^1=

    5*2 = 10

    3rd day = 20

    4th day = 40

    5th day = 80

    6th day = 160

    7th day = 320

    8th day = 640

    9th day = 1280 children
  2. 28 July, 23:14
    0
    Step-by-step explanation:

    8 days
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