Let's say that the 240 pennies removed from Debra's bank is x. So 7/10 - x = 1/2. Put another way, 7/10 - 1/2 = x. In order to subtract fractions there must be a common denominator. The common denominator of 10 and 2 is 10. Since 2 goes into 10 5 times, We must multiply 1/2 by 5/5. Since 5/5 = 1, we are just multiplying by 1 and not changing anything. So now we have 7/10 - 5/10 = x, which comes out to 2/10 = x. So 240 pennies will occupy 2/10 of the penny bank. To find out how many 2/10 are in the bank, we divide it into 1. So 1 ÷ 2/10 is the same as 1 × 10/2, which equals 5. 240 × 5 = 1200 pennies the bank can hold.
