Diagrams - GMAT Quantitative

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Question

Venn

Define the universal set .

Define to be the set of prime numbers, to be the set of integers that end in 2, 5, or 8, and . If each number in the universal set were to be placed in its correct region in the above Venn diagram, how many integers would lie in the gray region?

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Answer

The integers that go into the gray region are those that do not fall into any of the three sets , , or . We can eliminate the integers by taking the universal set and eliminating the elements that fall in any one of the three.

Out of the 50 integers from 1 to 50, we can eliminate the 20 that are in . This leaves 30 so far:

Now we can eliminate nine integers from - the ones that end in 2, 5, or 8. The 21 remaining numbers are

.

We now eliminate the primes from - 3, 7, 11, 13, 17, 19, 41, 43, 47. This leaves us with

,

a set with 12 elements.

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