Answer: 
Step-by-step explanation:
We know that the general form of the exponential decay formula is
, where y is final amount remaining after t time, A is the original amount and r is the rate of decay
Now, the ratio of strontium-90 remaining, p , as a function of years, t , since the nuclear accident. 
Hence, the ratio of remaining since the nuclear accident is 
Answer:
15
Step-by-step explanation:
Simply subtract the smaller number from the bigger number, and divide by 2. Or add the two numbers together and divide by 2.
The second one is the answer: f(4) = 22
Answer: 1 3/4
Step-by-step explanation: First, convert 4 1/2 and 2 3/4 to have like denominators.
4 1/2 = 4 2/4 because 1 x 2 = 2 and 2 x 2 = 4 = 2/4
2 3/4 stays the same.
Now, subtract 4 2/4 - 2 3/4 (4 x 4 = 16 + 2 = 18) and (2 x 4 = 8 + 3 = 11)
18/4 - 11/4 = 7/4 or 1 3/4