Each plant of a certain variety yields 50 seeds in the early fall and then dies. Only 40 percent of these seeds produce plants the following summer and the remainder never produce plants. At this rate, a single plant yielding seeds in 1986 will produce how many plants as descendants in 1989?

Answer 1

.4 * 50 = 20

20 + 20^2 + 20^3 + 20^4 = ?