Suppose strontium-90 decays at a rate of 2 percent per year.

Question

(a) Write the fraction P of strontium remaining, as function of t, measured in years. (Assume that at time t=0 there is 100 % remaining.)
Answer: P(t)=(.98)^t

(b) Estimate the half-life of strontium.

(c) If presently there is 6 grams of strontium, estimate how many grams of the substance will remain after 38 years.

i need help with b and c

Answer 1

write a formula,p(t), that models the percent of strontium-90 after t years.
:
The radioactive decay formula
A = Ao*2^(-t/h)
Where
A = resulting amt after t time
Ao - initial amt
h = half-life of substance
t = time of decay
:
To find percent here, you could write it
p(t) = 100*2^(-t/28)

Answer 2

a)
P = (.98)^t , you had that

b)
1/2 = .98^t
.5 = .98^t
take logs of both sides and use log rules ...
log .5 = t(log .98)
t = log .5/log .98 = appr 34.4 years

c) P = 6(.98)^38
= aprr 2.78 g

makes sense, since the half-life of 34.4 years would have reduced it to 3 g , and we went just a few more years.