If 
is the amount of strontium-90 present in the area in year 
, and it decays at a rate of 2.5% per year, then
Let 
be the starting amount immediately after the nuclear reactor explodes. Then
or simply
So that after 50 years, the amount of strontium-90 that remains is approximately
or about 28% of the original amount.
We can confirm this another way; recall the exponential decay formula,
where is measured in years. We're told that 2.5% of the starting amount 
decays after 1 year, so that
Then after 50 years, we have
Answer:
James
Step-by-step explanation:
James rate:
2x + 2 = 4
2x = 2
x = 1 hour
Rate = distance/time = 4/1 = 4 miles per hour
Craig's rate = 1/2 = 0.5 miles per hour
James is faster
