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SAT Question of the Day August 11th 2013

### If Kelly buys pens priced at dollars each and pens priced at dollars each, which of the following expresses, in terms of and , the average (arithmetic mean) price, in dollars, of these pens?

### A.

### B.

### C.

### D.

### E.

### Very similar to the question discussed in the previous post, we have a word to equation problem.

### One way (not recommended) is plug in and see that you obtain the number you expect to get.

### The better way, in my opinion, is to try and translate the problem.

### Lets say Kelly buys 4 pens, each for $2. She will pay for them $8. If she buys the other kind, lets say 5 of them, she will pay for each $4 and for these $4 pens she’ll pay $20.

### She bought 9 pens for a total of $28.

### Each pen, on average, will cost $28/9 which is a little less than $3.5

### This is the way to calculate a weighted average (where we care about the amount we have of each ingredient).

### If we follow the steps we just took using the letters t and u instead of the actual numbers it is clear we should mark D.

### 68% got it right.

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