Question

A certain colony of bacteria triples in length every 10 minutes. It's length is now 1 millimeter. how long will it be in 40 minutes?

Answer 1

So we know that the bacteria grows 3x as much every ten minutes.  From this we know that it'll be 3 mm in 20 minute.  Continuing the pattern, we can figure out that in 40 minutes the bacteria will be 81 mm.

The pattern: 10min - 3  20min - 9  30min - 27  40min - 81