Random Double Matrix Question #3

by on May 16th, 2011

International Double Matrix month is half over.  Have you become an expert at solving Double Matrix questions yet?

What’s a Double Matrix question?

For those who missed the first article in this series, a Double Matrix question (also known as an Overlapping Sets question) is one that involves a certain population where each member of that population has two characteristics associated with it.  Questions that fall into this category can often be solved using the Double Matrix Method.

For an introductory lesson on the Double Matrix Method, please watch the video at http://www.youtube.com/watch?v=OWD2t5jCCZQ

Afterwards, you can try solving this super difficult question:

In a group of 1000 people, each person is either left-handed or right-handed but not both.  80% of the females are left-handed, and 84% of the right-handed people are male.  How many people are right-handed?

1) There are 600 males in the group

2) There are 180 left-handed males in the group

Once you’ve attempted the question, you can watch the video solution below:

YouTube Preview Image




  • I just want to point out, that if we denote the number of right-handed females by X, then the number of left-handed females is 4X (80=4x20). Since X also represents 16% of those who are right-handed, then the number of right-handed males is 5.25X (84=16x5.25). So, the number of left-handed males is 1000-10.25X. Then each piece of information can be translated into an equation in X, which can allow the computation of any of the quantities. Therefore the answer is obviously D. Very nice method the use of the 2x2 matrix, thank you!

  • Thanks for showing that the question can be solved using 1 variable as well, Eva!

  • Such a amazing question that both statements are individually sufficient.


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