a certain variety of strawberry plant sends out an average of 5 new runners per plant each year. If you planted 20 of these plants, how many strawberry plants would you have after 4 years?
Each year there are 5 new plants for every exiting plant. That means the number grows by a factor of 6 each year.
If a n runner produces a plant every time,
6^4 = 1296
20*6^4 = 25920
pretty crowded, eh?