Step-by-step explanation:
The half-life period is represented by the abbreviation P. The time that a material has suffered disintegration is represented by t. Thus, if we know the half-life and the disintegration time (represented by x), we can say how many half-lives a material has gone through until a certain moment. This is done through the relationship below:
t = x * P
With this knowledge, we can still determine the mass that remains after the half-life period from the expression:
m = mo/2^x
were m = mass left
mo = initial mass
x = half-life
Here we have:
P = 9 minutes
t = 27 minutes
x = ????
mo = 80 g
So first let's find x:
t = x*P
27 = x*9
x = 3
now let's find m:
m = mo/2^x
m = 80/2^3
m = 80/8
m = 10 g
Answer: b. 10