A radioactive element has a half-life of 6.41 days. What percent of the original sample will be left after 15.0 days?

Answer 1

estimate: that is over 2 half lives, guessing 20 percent. The math

amountremaining=original*e^(-ln2*15/6.42)

decimal percent=e^(-ln2*15/6.42)=.199
or 19.9 percent

Answer 2

Thanks