GMAT Question of the Day – Data Sufficiency – Overlapping Sets 1
At a certain company, 1/3 of the employees are senior managers and 2/3 of the employees are full-time. If 1/5 of the full time workers contribute to the company retirement plan, how many of the full-time employees contribute to the company retirement plan?
(1) Exactly 120 of the employees are senior managers
(2) Of the full-time employees, 3/4 of them are not senior managers
GMAT Question of the Day Solution:
For overlapping sets with 2 groups (in this case Senior Managers and Full Time Employees) use a chart (see below). Take your time organizing the information. Read carefully.
Overlapping sets Strategies and Organization:
1. It helps to make 1 chart per statement so that you don’t confuse the information. Using one chart and erasing the information from the first statement so that you can evaluate the second statement is a chaotic waste of time. In this case I didn’t make a chart for statement (2) because I could clearly see that it was insufficient.
2. If you don’t have a total then make that a variable. I always use T.
3. Use a box to highlight the space in the chart that you are solving for. Here I put a question mark above the box but only for demonstration purposes. Avoid putting a question mark in your chart – it’s messy and takes up space.
4. Last thing – avoid doing calculations in the box. Do those off to the side and then fill in the chart with the values.
Here’s a challenging sets question from the GMAT Prep Tests 1 and 2. Stay organized. Make the easy inferences and you should be fine.
In a certain city, 80 percent of the households have cable television, and 60 percent of the households have videocassette recorders. If there are 150,000 households in the city, then the number of households that have both cable television and videocassette recorders could be any number from:
Here’s an overlapping sets question that adds in a bit of probability. Don’t let the probability component get in your way! Often, probability questions are easy. Take it step by step.
Among a group of 2,500 people, 35 percent invest in municipal bonds, 18 percent invest in oil stocks, and 7 percent invest in both municipal bonds and oil stocks. If 1 person is to be randomly selected from the 2,500 people, what is the probability that the person selected will be one who invests in municipal bonds but NOT in oil stocks?
Here’s one from GMAT Question of the Day that’s very similar in that the answer is based on proportions. It doesn’t have a probability component but again: same idea and great practice.
And here’s a very tough DS overlapping sets questions. Again, deals with counting equations/system of questions.