1. The half-life, T, for a particular radioactive element is 3 min. Find the decay rate of the element.

The decay rate is ____?% per min. (Do not round until the final answer. The round to the nearest tenth as needed.)

2. Uranium-238 (U-238) has half-life of 4.5 billion years. Geologists find a rock containing a mixture of U-238 and lead, and determine that 79% of the original U-238 remains; the other 21% has decayed into lead. How old is the rock?

The rock is _____? billion years old.

(Round to three decimal places as needed.)

3. An athlete signs a contract guarantees a $13-million salary 7 years from now. Assuming that money can be invested at 6.8% with interest compounded continuously, what is the present value of that year's salary?

$_____? (Round to the nearest dollar as needed. Do not include the $ symbol in your answer.)