If there are 360 g of radioactive material with a half life (decreased by half or 50% )of 1 hour, how much of the radioactive material will be left after 4 hours ?

After 1 hour, 360 g decays to 180 g.

After another hour (total 2 hours), 180 g decays to 90 g.

After another hour (total 3), 90 g decays to 45 g.

After one more (total 4), 45 g decays to 22.5 g.

More quickly, with a half-life of 1 hour, the 360 g of starting material decays to

(360 g) / 2⁴ = 22.5 g

In general, if the half-life is 1 hour, then after n hours, an initial amount A of this substance decays according to

A / 2ⁿ