A dragon lived in a cave. The dragon doubled in size every day.
After 20 days the dragon filled the cave.
After how many days did the dragon half-fill the cave?

After 19 days, the dragon filled half of the cave.

Step-by-step explanation:

The dragon doubled in size every day and after 20 days he filled the cave.

So, one day before, the dragon occupied half of the cave.

20 - 1 = 19  [days]

$650 per month plus utilities

step-by-step explanation:

just based on the info you gave, it would seem more cost effective to rent at $650 per month plus utilities.   if utilities are, in fact, $150 per month, your monthly living costs would be $800 as opposed to the other option of $825.