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Re: If n is an integer, which of the following CANNOT be
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21 Nov 2017, 10:04
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chintzzz wrote:
If n is an integer, which of the following CANNOT be a factor of 3n+4?
A. 4 B. 5 C. 6 D. 7 E. 8
KEY CONCEPTS If a number is divisible by 6 it MUST also be divisible by 3 Conversely, if a number is NOT divisible by 3, then that number is NOT divisible by 6
3n + 4 = 3n + 3 + 1 = 3(n + 1)+ 1 We can see that 3n+4 is 1 greater than some multiple of 3 This tells us that 3n+4 is NOT divisible by 3 This means (from the rules above) that 3n+4 is NOT divisible by 6
Re: If n is an integer, which of the following CANNOT be
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26 Sep 2019, 06:54
A simple but effective method in solving this question would be to plug in simple values for n and eliminate options which can be factors of 3n + 4. It can also be a very efficient method to save time.
If n = 0, then 4 can be a factor of 3*0 + 4. Option A can be eliminated.
If n = 1, 7 can be a factor of 3*1 + 4. Option D can be eliminated.
If n = 2, 5 can be a factor of 3*2 + 4. Option B can be eliminated.
If n = 4, 8 can be a factor of 3*4 + 4. Option E can be eliminated.
The option left is C. It has to be the right answer.
Note: Remember to use the PEMDAS rule when you are evaluating the expression after plugging in values.
Re: If n is an integer, which of the following CANNOT be
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30 Sep 2019, 08:37
Solution
Approach and Working out
If 3n+4 is divisible by a number, then that number will be the factor of 3n+4. Now, 3n +4 = 3(n+1) +3 = 3k +1 And, 3k+1 will never be divisible by 3 or by any multiple of 3. In options, only multiple of 3 is 6. Hence, 6 will never be a factor of 3n+4.
Thus, option C is the correct answer. Correct Answer: Option C _________________
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66% (01:26) correct 
