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Topaz
Lv 5
Topaz asked in Science & MathematicsMathematics · 6 years ago

Logarithm help?

Update:

A person moves 10% of her way each hour. How long does it take to complete half of his way?

I have no idea how to set this problem, but I know we are supposed to use logarithms in it somehow. Can someone please help? Thanks!

3 Answers

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  • DWRead
    Lv 7
    6 years ago
    Favorite Answer

    If the question is stated accurately, it takes 5 hours. But that is too easy.

    I think it's supposed to be 10% of the distance in the first hour,

    10% of the remaining distance in the second hour,

    10% of the remaining distance in the third hour,

    etc.

    x = starting distance

    0.10x traveled in the first hour; 0.90x distance remains.

    0.10(0.90x) traveled in the second hour; 0.90(0.90x) distance remains.

    0.10(0.90²x) traveled in the third hour; 0.90(0.90²x) distance remains.

    etc.

    After n hours, 0.90³x distance remains.

    0.90ⁿx = 0.5x

    0.90ⁿ = 0.5

    take log base 0.90 of both sides

    n = 6.578813479

    It takes about 6.6 hours to travel halfway.

  • Anonymous
    6 years ago

    I don't see the use of logarithms into this.It seems a simple problem,

    If 10 % of his/her journey is completed in 1 hour than remaining 90 % will be completed in 9 hrs.So,the total time required to complete journey will be 9+1 =10 hrs.

    So ,half of the journey will be done in 10/2=5 hrs.

  • Anonymous
    6 years ago

    if a person moves 10% of the distance in one hour, then 90% remains...

    (0.90)^n = (0.50)

    n log (0.90) = log (0.50)

    n = [log (0.50)]/[log (0.90)] ≈ 6.5788 hours

    check...do something

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