A football game was played between two teams, the Cougars and the Panthers. The two teams scored a total of points, and the Cougars won by a margin of points. How many points did the Panthers score?
- A)
- B)
- C)
- D)
- E)
Answer
A
Key insight
Take away the 14-point winning margin from the total 34. What is left, 20, is split equally between the two teams, so the losing team has 10.
Solution
- The Cougars won, so they scored more points than the Panthers.
- Picture taking those extra points away from the Cougars. Then both teams have the same score, and the total drops to .
- Two equal scores that add to are each. That equal score is exactly the Panthers' score, since we only took points away from the Cougars.
- Check: the Cougars scored . Then and . Both facts match.
The Panthers scored .
Why this works
When you know the total of two amounts and how far apart they are, remove the difference, split what is left in half, and you have the smaller amount. Add the difference back to get the larger one. Always reread the question to see which of the two it wants.
Alternative approach
With letters: let be the Cougars' score and the Panthers'. Then and . Adding the two equations gives , so , and then .
The trap
Answering 24, which is the Cougars' score, when the question asks for the Panthers, the team that lost.
Concise solution
Let and be the Cougars' and Panthers' scores. We know and .
Subtracting the second equation from the first eliminates :
(Then , and indeed and .)
The Panthers scored .
Review in the AoPS books
- Introduction to Algebra, Chapter 3: One-Variable Linear Equations (§3.3, §3.4)
- Introduction to Algebra, Chapter 5: Multi-Variable Linear Equations (§5.2, §5.3, §5.6)
- Introduction to Algebra, Chapter 7: Proportion (§7.4)
- Intermediate Algebra, Chapter 1: Basic Techniques for Solving Equations (§1.4)
Techniques
Set up the equation/formula and compute; no special trick needed