Question

Grandma bakes the world’s best and favorite cookies. Grandma’s cookies have a half life of 2 hours. One day, Grandma baked a lot of cookies. If 2 days and 6 hours later, 2 cookies still remain, how many cookies did Grandma bake?

Answer 1

2 = 36(18)t/2

1/18 = (18)t/2

ln(1/18) = (t/2)ln18

2ln(1/18) = tln18

t = 2ln(1/18)/ln18