Answer
The measure of the yeast culture for the end of the next 5 days is 1280.
For the measure of the yeast culture at least 10,000, the number of days to take is 8.
Work Step by Step
The situation can be modeled by a geometric series with $a_{1} = 80$ and $r = 2$, whose general term $a_{n} = 80(2)^{n-1}$ where n = number of days ending.
The measure of the yeast culture for the end of the next 5 days, n=5, is $a_{5} = 80(2)^{5-1} = 1280$
For the measure of the yeast culture at least 10,000, the number of days to take will be represented by
$10000 \leq 80(2)^{n-1}$
$125 \leq (2)^{n-1}$
$250 \leq 2^n$
$n \geq 8$
The least number of days = 8
