Question

Isotope X has a half-life of 8.00 minutes. How much of a 75.0 g sample will remain

after 32.0 minutes?

Answer 1

After 8.00 min, 75.0/2 = 37.5 g of the sample remains.

After another 8.00 min (total 16.0 min), 37.5/2 = 18.75 g remains. (Equivalently, 75.0/2^2 g)

After another 8.00 min (total 24.0 min), 18.75/2 = 9.375 g remains. (Or 75.0/2^3 g)

Finally, after another 8.00 min (total 32.0 min), 9.375/2 = 4.6875 g remains (or 75.0/2^4 g), approximately 4.69 g.