Sandwiches at Joe's Fast Food cost each and sodas cost each. How many dollars will it cost to purchase sandwiches and sodas?
- A)
- B)
- C)
- D)
- E)
Answer
A
Key insight
Find the cost of the sandwiches and the cost of the sodas separately, then add the two amounts.
Solution
Work out each kind of food on its own line, then add.
- Sandwiches: sandwiches at each cost dollars.
- Sodas: sodas at each cost dollars.
- Together: dollars.
The answer is .
Why this works
When you buy several kinds of things, the bill is (how many) times (price of one) for each kind, added up. Writing each kind on its own line makes it easy to check that every price goes with the right item.
The trap
Mixing up the prices, paying 2 dollars per sandwich and 3 per soda. That gives 10 + 24 = 34, the wrong choice (D).
Concise solution
Five sandwiches at apiece come to dollars. Eight sodas at apiece come to dollars.
Adding the two subtotals gives dollars.
The answer is .
Review in the AoPS books
- Introduction to Algebra, Chapter 3: One-Variable Linear Equations (§3.3, §3.4)
- Introduction to Algebra, Chapter 7: Proportion (§7.4)
Techniques
Set up the equation/formula and compute; no special trick needed