Use the number properties :
e=even ; o=odd
e+e=e
e+o=o
o+o=e
Is the answer C ?? I got A
Sub 1) in the a-3b , you get -(8a+9) which is odd
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what is the best way to solve such problems?
Source: Beat The GMAT — Data Sufficiency |
Is a-3b even?
A. b=3a+3
a may be odd / even.
If a is odd, b = odd + odd = even. a-3b is odd. NO
If a is even, b = even + odd = odd. a-3b is odd. No
Sufficient.
B. b-a is odd
We have 2 possibilities,
i. odd-even = odd
then a-3b = even - odd = odd. NO
ii. even-odd = odd
then a-3b = odd - even = odd.NO
Sufficient.
Must be D
A. b=3a+3
a may be odd / even.
If a is odd, b = odd + odd = even. a-3b is odd. NO
If a is even, b = even + odd = odd. a-3b is odd. No
Sufficient.
B. b-a is odd
We have 2 possibilities,
i. odd-even = odd
then a-3b = even - odd = odd. NO
ii. even-odd = odd
then a-3b = odd - even = odd.NO
Sufficient.
Must be D
i also feel D is correct option..
1). b=3a+3
if a=2 then b=9
a-3b=-25
if a=3 then b=12
a-3b=-33
hence sufficient
2). b-a is an odd number
b=5,a=2
a-3b=-13
b=6,a=3
a-3b=-15
hence sufficient
1). b=3a+3
if a=2 then b=9
a-3b=-25
if a=3 then b=12
a-3b=-33
hence sufficient
2). b-a is an odd number
b=5,a=2
a-3b=-13
b=6,a=3
a-3b=-15
hence sufficient
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1). b=3a+3
2). b-a is an odd number
interestingly, 2) can be derived from 1)
1) b=3a+3 or b-a = 2a + 3 , 2a is even so 2a + 3 has to be odd
so b-a is a odd no evident in statement 1) itself.
2). b-a is an odd number
interestingly, 2) can be derived from 1)
1) b=3a+3 or b-a = 2a + 3 , 2a is even so 2a + 3 has to be odd
so b-a is a odd no evident in statement 1) itself.
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Stuart@KaplanGMAT
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Everyone seems to be making a big assumption!
Do your proofs hold true if a and b are non-integers?
Do your proofs hold true if a and b are non-integers?
Stuart Kovinsky | Kaplan GMAT Faculty | Toronto
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The point about non-integers just increased the difficulty of this problem by a lot.
What's the most efficient method of tackling this problem?
Picking numbers could take you years to solve this one.
What's the most efficient method of tackling this problem?
Picking numbers could take you years to solve this one.
Hello Stuart,Stuart Kovinsky wrote:Everyone seems to be making a big assumption!
Do your proofs hold true if a and b are non-integers?
How can we test this for fractions?
Thanks
