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
option D none of the above
answer= x=20
Step-by-step explanation:
We have, 35% × x = 7
or,
35
100
× x = 7
Multiplying both sides by 100 and dividing both sides by 35,
we have x = 7 ×
100
35
x = 20
If you are using a calculator, simply enter 7×100÷35, which will give you the answer.
there is 60 seconds in 1 min so if you do 60x9 you should get 540
glad to help!
