Exponential and Logarithmic functions

posted by Sara

A certain material decays at a rate of 1.9% per year. The sample is 260 grams. How much will be left in 11 years? How long will it take to have only a 100g sample left?

  1. Reiny

    decay rate = 1.9% = .019

    amount of the 260 g left after 11 years
    = 260(.981)^11
    = ...

    b) when are left with 100 g ?

    260(.981)^n = 100
    .981^n = .384615...
    take log of both sides and use log rules:

    n log .981 = log .384615...


  2. Sara

    Thank you

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