Calcium-47, used to evaluated bone metabolism, has a half-life of 4.5days: how many milligrams of a 16mg sample of calcium-47 remain after 18 days?

For this problem, we use the formula for radioactive decay which is expressed as follows:

An = Aoe^-kt

where An is the amount left after time t, Ao is the initial amount and k is a constant. 

We calculate as follows:

An = Aoe^-kt
0.5 = e^-k(4.5)
k = 0.1540

An = Aoe^-kt
An = 16e^-0.1540(18)
An = 1.00 mg

Hope this answers the question. Have a nice day.

a compound is a molecule made of atoms from different elements.

a. by the combination of an unlimited number of elements