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## Homework Statement

The half life of U-238 is approximately 4.4 billion years, while U-235 is approximately 700,000,000.

A Uranium ore has 0.75% U-235.

Assuming there was an even amount of both types of Uranium when the Earth was formed, estimate the age of the Earth.

## Homework Equations

N = N

_{0}- kt

where

N = amount after time t

N

_{0}= amount at time=0

k = decay constant

t = time

## The Attempt at a Solution

I don't do a lot of derivation at my school, but I want to get a lot better at it.

N = N

_{0}- kt

dN / dt = -kt

dN = -kt dt

∫ - kt dt (definite integral from t to t

_{0}

= -k(t - t

_{0})

I'm not really sure to go from here.