Answer:
19
Step-by-step explanation:
In the first day the population will decrease to 1530, then 1500 the day 2, 1470 day 3, and so on ...
For decrease and get less than 1000 the mold population needs to be reduced in at least 560. The questions turns to be, how many days will it take to reduce the population in 560 spores?
If we divide 560 between 30 it will gives us the answer:
560/30 = 18.667
So, it is need to wait 19 days. In 18 days only 540 spores are reduced. In 19 days 570. We will say 19 days as we are looking (I guess) for an integer number.
