4. Thorium-234 has a half-life of 24.1 days. What percentage of the original thorium-234 in a sample will remain after 144.6 days?

How many half lives have elapsed?

actually the formula is like this

A=P (1/2) ^ (t/h)

P=iniital amount

t=time

h=half life

A=final amount

so

hmm, percent

so P=1 then

A=1 (1/2) ^ (144.6/24.1)

A=1 (1/2) ^6

A=1/64

A=0.05625

so 5.625% is left