SAT Math Multiple Choice Question 766: Answer and Explanation
1. Lauren's car can travel d miles per gallon of gasoline. If she travels at a constant speed of s miles per hour, which of the following represents the number of hours she can travel on 6 gallons of gasoline?
Correct Answer: A
Algebra (rates) MEDIUM
Although this problem can be solved by "plugging in" convenient numbers for the unknowns, it is actually much more straightforward to treat this as a conversion problem, as discussed in Chapter 7, Lesson 4. The question gives us the "initial fact" that Lauren has 6 gallons of gas in her car, and we'd like to "convert" that fact into the number of hours she can travel. Using the rates given in the problem, the conversion should look like this:
Notice that all the units on the left-hand side cancel except for hours, which is the desired unit.