Today’s SAT question of the day is a math question about averages.

If Kelly buys t pens priced at 2 dollars each and u pens priced at 4 dollars each…what is the average price, in dollars, of these pens in terms of t and u?

Let’s think back to the general formula for averages:(sum of terms) / (number of terms) = average

In this case, Kelly buys a total of t + u pens, so that is the number of terms (our denominator).

How much does she spend on the pens?  Well, every t pen costs $2, so the total cost of those pens is 2t. Similarly, every u pen costs $4, so the total cost of those pens is 4u. Putting the cost of each pen together, our total cost is 2t + 4u.

The average cost per pen, then, is (2t + 4u) / (t + u).  If you take the problem one step at a time, it is really pretty simple!