Question

Suppose that unstable isotope A has a half life of 40 days and decays into the stable isotope B. If 120,000 atoms of isotope A were prepared, how many atoms of isotope B will be present once 120 days have passed?

Answer 1

Below

Step-by-step explanation:

120 days = 3 half lives of 40 days

so the count of A will go 120 000 ==> 60 000==> 30 000==> 15 000

the isotope A that changed to B is then:

120 000 - 15000 = B count = 105 000