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?
Your title says it's pretty simple. Why haven't you solved it then?
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: