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07 May 2021, 04:45
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C
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
45%
(medium)
Question Stats:
66% (01:47) correct
34%
(01:41)
wrong
based on 218
sessions
History
Date
Time
Result
Not Attempted Yet
If a and b are positive integers, which of the following cannot be an integer?
A. (2b)/(4a+1)
B. (2b)/(3a+1)
C. (2a+1)/(4b)
D. (2a+1)/(4b+1)
E. (2a·b)/(4b+2)
A. (2b)/(4a+1)
B. (2b)/(3a+1)
C. (2a+1)/(4b)
D. (2a+1)/(4b+1)
E. (2a·b)/(4b+2)
08 May 2021, 08:30
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Bunuel
I'd first look for an option which gives odd/even for any values of a and b, because odd/even is not an integer.
Option C fits: \(\frac{2a+1}{4b}=\frac{even+odd}{even}=\frac{odd}{even}\neq{integer}\).
Answer: C.
To discard other A consider a=5 and b=1.
To discard other B consider a=2 and b=1.
To discard other D consider a=2 and b=1.
To discard other E consider a=3 and b=1.
General Discussion
07 May 2021, 05:19
Kudos
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Thing to remember for this question: There are cases where an even number can be divided by an odd number (eg. 30/3 = 10), however, an odd number cannot be divided by an even number to give an integer.
Looking at the answers:
A. (2b)/(4a+1) will be even/odd ✓
B. (2b)/(3a+1) will be even/odd or will be even/even ✓
C. (2a+1)/(4b) will be odd/even ✖
D. (2a+1)/(4b+1) will be odd/odd ✓
E. (2a·b)/(4b+2) will be even/even ✓
Answer C
Looking at the answers:
A. (2b)/(4a+1) will be even/odd ✓
B. (2b)/(3a+1) will be even/odd or will be even/even ✓
C. (2a+1)/(4b) will be odd/even ✖
D. (2a+1)/(4b+1) will be odd/odd ✓
E. (2a·b)/(4b+2) will be even/even ✓
Answer C
