If S seniors were going to split a $1000, then they were each going to pay 1000/S. Now, since 20 people aren't going to pay, everyone has to pay 1000/(S-20). The difference between the two amounts is:
Solve that and you'll have your answer.
The senior class decided to have a picnic. A total of S seniors pledged to contribute equally for the $1000 fund. If 20 refused to honor their commitment, how much more would each of the rest of the seniors have to pay?
Let S = # seniors total
Let S - 20 = # seniors that actually contributed
Initially, each contributer promised to give
Later, after 20 reneged, it changed to
The amount extra that the S - 20 group had to give was:
Consider the following example:
Suppose S = 100
Initially, each would give 1000/100 = $10
Later, only 100 - 20 or 80 commited, so the new amount per senior = 1000/80 = $12.50.
The difference = $2.50 more.
Check it using the formula derived: