Terbium-160 has a half-life of about 72 days. after 396 days, about how many milligrams of a 220 mg sample will remain? a. 5 mg b. 12 mg c. 40 mg d. 194 mg

Option A = 5 mg  

Step-by-step explanation:

Given : Terbium-160 has a half-life of about 72 days.

To find : After 396 days, about how many milligrams of a 220 mg sample will remain?

Solution :

We have given the Terbium-160 has a half-life of about 72 days.  

We can represent the situation with an exponential function,

Where,

is the amount at any time t,

is the original amount,

n=72 is the half-life

t=365 number of days

Substituting all the values,

Approximately 4.84=5 mg

Therefore, Option A is correct.  

After 396 days, there will only be 5 mg of Terbium-160.                        

the answer would be a 24

step-by-step explanation:

c=2πr=2·π·3=24