I need help with this science hw.?

Question

One half of the radioactive potassium -40 (K^40) in an igneous rock has decayed to argon -40 (Ar^40) About how many years ago was this rock formed?

1. 1.3x10^9

2. 2.6x10^9

3. 3.9x10^9

4. 9.8x10^9

Uranium-238 is used to date the age of Earth rather that carbon-14 because uranium-238

1. was more abundant when Earth formed

2. has a longer half-life

3. decays at a constant rate

4. is easier to collect and test.

Also I dont get these questions

When the quantity of a radioactive material decreases, the half life of that substance will?

1. decrease

2. Increase

3. remain the same.

As the temperature of a radioactive substance increases the rate at which the substance will disintegrate

1. increase

2. decreases

3. remains the same

I really dont get these its not that I dont want to do my hw

Answer 1

http://nemo.sciencecourseware.org/Virtua... this will help you learn how to do all of this.