Bunuel wrote:
How many of the 90 laptop computers sold in January by online retailer DigiComputerz had neither a DVD/Blu-ray player nor dual-CPU capability?
(1) Of the 90 laptops sold, 30 had dual-CPU capability but no DVD/Blu-ray player.
(2) Of the 90 laptops sold, 45 had both a DVD/Blu-ray player and dual-CPU capability.
Target question: How many of the 90 laptop computers sold in January by online retailer DigiComputerz had neither a DVD/Blu-ray player nor dual-CPU capability?One approach is to use the
Double Matrix Method. This technique can be used for questions featuring a population in which each member has two characteristics associated with it (aka overlapping sets questions).
Here, we have a population of 90 laptop computers, and the two characteristics are:
- have a DVD/Blu-ray player or don't have a DVD/Blu-ray player
- have dual-CPU capability or don't have dual-CPU capability
So, we can set up our matrix as follows:
Aside: Notice that I placed a star in the box representing neither a DVD/Blu-ray player nor dual-CPU capability. This is the value we are seeking to find. At this point, when I scan the two statements, they certainly don't seem sufficient on their own. So, I’m going to head straight to……
Statements 1 and 2 combined Statement 1 tells us that 30 laptops had dual-CPU capability but no DVD/Blu-ray player.
Statement 2 tells us that 45 laptops had both a DVD/Blu-ray player and dual-CPU capability.
When we add this information to our matrix, we get:
As you can see, there are several different ways to complete the remaining two boxes so they all add up to 90.
Here are two possibilities:
In the first example, the answer to the target question is
5 laptops had neither a DVD/Blu-ray player nor dual-CPU capabilityIn the second example, the answer to the target question is
10 laptops had neither a DVD/Blu-ray player nor dual-CPU capabilitySince we can’t answer the
target question with certainty, the combined statements are NOT SUFFICIENT
Answer: E
This question type is
VERY COMMON on the GMAT, so be sure to master the technique.
To learn more about the Double Matrix Method, watch this video:
EXTRA PRACTICE QUESTION
More questions to practice with:
EASY:
https://gmatclub.com/forum/of-the-120-p ... 15386.html MEDIUM:
https://gmatclub.com/forum/in-a-certain ... 21716.html HARD:
https://gmatclub.com/forum/a-group-of-2 ... 24888.html KILLER:
https://gmatclub.com/forum/a-certain-hi ... 32899.html