Half life earth science help? 10 pts best answer?

Question

I dont know how to do my study guide...
its for earth science

Uranium-235 (the parent material) decays to Lead-207 (the daughter product) with a
half-life of 7.13 million years. Using the half-life provided, calculate
how old a substance is if it contains the following percentages.
a) 75% U-235: c) 50% Pb-207
b) 6.25% U-235: d) 12.5% Pb-207

I just need help with one of each...

Answer 1

It's an exponential equation

Conc. U sub 235 = 1/ (2^T) in units of 7.13 Mil yrs)

Now with 50% Pb it's easy (50% Pb means 50% U)

T =1 or 7.13 x 10^6 yr.s

It's an exponential curve so for the fractions you need to solve the equations

75% u WILL NOT indicate 1/2 of that half life period.

Answer 2

Age = (half-lives elapsed) * (7.13E6 y)

The number of half-lives elapsed for each is:

a) 1/2

b) 4

c) 1

d) 1/4

multiply each by 7.13 million years to calculate age

Answer 3

First you must have an understanding of that you are asking this query in the "movies" forum... Just that fact by myself i might offer you an F... Additionally, you are ready except the final minute, F- In the USA, the cutting-edge craze is substitute vigour. Probably you must do some thing about the internet or you can do a paper on the "Psychology of Procrastination". Each will have to be a benefit for you.