How would you solve this popular type of GMAT question?

A parking lot contains 80 vehicles. Each vehicle is either a car or a truck, and each vehicle is either red or green. 35 vehicles are red, and 60 vehicles are cars. If there are 9 green trucks, how many red cars are there?

Students typically use a Venn diagram here, but another option is to use a technique known as the Double Matrix Method. This technique is great for organizing information, and it is particularly useful when tackling advanced questions of this type.

See what you think.