# 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...

continue

2. Sara

Thank you

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