- #1

pinnacleprouk

- 26

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**Logarithim question "decreasing in value"**

## Homework Statement

The Radioactivity (R) of a substance can be modeled using the equation:

R = A x 2 ^ -Bt

Where R is measured in becquerels per gram, t is measured in hours and A and B are constants.

If a substance has an initial radioactivity of 60 becquerels and one hour later it is 50 becquerels find A and B and the time for the radioactivity to reduce to half its initial value (Half Life)

## Homework Equations

R = A x 2 ^ -Bt

## The Attempt at a Solution

R = A x 2 ^ - Bt

R = 60 t = 0

R = 50 t = 1

60 = A x 2 ^ - Bx0

60 = A

50 = 60 x 2 ^ - B

2 - B = 50/60

2 - B = 0.8

log 2 - B = log 0.8

- B log 2 = log 0.8

- B = log 0.8/log 2

- B = - 0.32

Is this all right?

I work out half life to be around 3 hours but could anybody give me a more exact time?

Thanks in advance