Which of the following is NOT a factor of 20! ?
I. 29
II. 85
III. 121
A. I only
B. II only
C. III only
D. I and II
E. I and III
The OA is E.
Is there a fast way to get the correct answer here? Experts, can you show me how would you solve it? Thanks in advanced.
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Which of the following is NOT a factor of 20! ?
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EconomistGMATTutor
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Hello Vincen.
Let's take a look at your question.
Option 1) 29.
This is a prime number and it does not appear in 20! So, this is not be a factor.
Option 2) 85.
85=5*17, and 5 and 17 are in 20! So, 85 is a factor.
Option 3) 121.
121=11*11, but in 20! there is only one 11. So, this is not be a factor.
Therefore, the correct answer is E.
I hope this explanation may help you.
I'm available if you'd like a follow-up.
Regards.
Let's take a look at your question.
Option 1) 29.
This is a prime number and it does not appear in 20! So, this is not be a factor.
Option 2) 85.
85=5*17, and 5 and 17 are in 20! So, 85 is a factor.
Option 3) 121.
121=11*11, but in 20! there is only one 11. So, this is not be a factor.
Therefore, the correct answer is E.
I hope this explanation may help you.
I'm available if you'd like a follow-up.
Regards.
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Jeff@TargetTestPrep
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Since 20! does not contain a prime factor of 29, 29 is not a factor of 20!Vincen wrote:Which of the following is NOT a factor of 20! ?
I. 29
II. 85
III. 121
A. I only
B. II only
C. III only
D. I and II
E. I and III
Since 85 = 17 x 5, and 20! contains both prime factors of 17 and 5, 85 is a factor of 20!.
Since 121 = 11^2, and 20! does not have 2 prime factors of 11, 121 is not a factor 20!.
Answer: E
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