Amanda's penny bank is 23 full. After she removes 120 pennies, it is 12 full. How many pennies can Amanda's bank hold?

So if the bank was 2/3 full, and then after the pennies are removed it is 1/2 full, then the volume taken up by those removed pennies is the difference:

(2/3) - (1/2) = (4/6) - (3/6) = 1/6

If there are 120 pennies in 1/6 of the bank's volume, then the total can be found by multiplying 120 by 6 (so that (1/6) * 6=1 (the total volume))

120*6=720

You can fit 720 pennies in that bank