Question

I have no idea how to solve these.
Plus there's another question that is

2) A 10 kilogram meteorite is collected in space and brought back to Earth. It is composed of 1.25 kg of Uranium-238 and 8.75 kg of Lead-206.
How many U-238 half lives have passed?
What is the approximate age of the meteorite?

Answer 1

Half life is the period of time it takes for one-half of the atoms of an original isotope to decay.

$formula=(\frac{1}{2})^{n}$

In this example we have:  $(\frac{1.25 kg}{10kg})^{n}$ where n= the number of half lives.

Thus: $\frac{1.25kg}{10kg} =\frac{1}{8}$

$\frac{1}{8} =(\frac{1}{2})^{n}$ From this equation n=3. The answer to your question is: 3 half lives have passed which gives the meteorite an age of 4.5*3= 13.5 billion years.