Morea on applications of differential equations.

1. The bacteria in a certain culture increase continuously at a rate
proportional to the number present.
(a) If the number triples in 6 hours how many are there in 12 hours?
(b) In how many hours will the original amount quadruple?

4. Radium decomposes at a rate proportional to the amount present. Find
an expression for the amount R left after t years, if R is present
0
initially and c is the negative constant of proportionality.