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Set B contains all factors and multiples of 20. If x is

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by AAPL » Thu May 31, 2018 4:58 am

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Set B contains all factors and multiples of 20. If x is divided by 20, then x must also be divisible by how many members of set B?

A. 4
B. 5
C. 6
D. 10
E. 20

The OA is C.

Factors of 20 = 1, 2, 4, 5, 10, 20
Multiples of 20 = 20, 40, 60, 80, . . . . . . . . . .

So, B={1, 2, 4, 5, 10, 20, 40, 60, 80, . . . . . . . . . . . . .}

x/20 = remaider 0.

Let the minimum value of x = 20

Thus x must be divisible by 1, 2, 4, 5, 10, 20

So, x must also be divisible by 6 members of set B. Option C.

Has anyone another strategic approach to solve this PS question? Regards!
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Source: — Problem Solving |

by swerve » Thu May 31, 2018 10:20 am
x is divisible by 20 means that x is definitely divisible by all factors of 20. But we can't be sure about divisibility of x by other multiples of 20: 20*2, 20*3 .... Our B is infinite set {0; +∞}, but we are definite only with part of it's elements, which represent factors of 20.

20 = 2^2 * 5

# of factors = 3*2 = 6.

The correct answer is the option C.

Regards!
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by Jeff@TargetTestPrep » Fri Jun 01, 2018 11:57 am
AAPL wrote:Set B contains all factors and multiples of 20. If x is divided by 20, then x must also be divisible by how many members of set B?

A. 4
B. 5
C. 6
D. 10
E. 20
If x is divisible by 20, then it MUST BE divisible by all the factors of 20. The factors of 20 are: 1, 2, 4, 5, 10 and 20. So x must also be divisible by 6 members of set B.

Answer: C

Jeffrey Miller
Head of GMAT Instruction
[email protected]

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