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Is a-3b an even number?
Source: Beat The GMAT — Data Sufficiency |
b-a is odd
For the difference to be odd one number should be odd and other even
So either b is odd or a is odd, but both of them are not odd and not even
b=8 a =3 b-a =5 is odd a-3b =3-24 = -21 Not even
b=5 a=8 b-a =-3 is odd a-3b = 8-15 = -7 Not even
b=5 a=0 b-a =5 is odd a-3b = -15 Not even
b=0 a=7 b-a =-7 is odd a-3b = 7 Not even
b=7 a=-4 b-a =11 is odd a-3b =-4-21 =-25 Not even
Looks like B or D is the answer
b=3a+3
Substitute b in a -3b=a-3(3a+3)= a-9a-9 = -8a-9
a =-2 -8a-9 = 7 Not even
a =-1 8-9 =-1 Not even
a = 0 0-9 = -9 Not even
a =1 -8-9 =-17 Not even
a=2 -16-9 = -25 Not even
We can definitively say that a-3b is Not even. we have sufficiency in both cases. Correct me if I went wrong with numbers some where.
Thanks for the good Questions
For the difference to be odd one number should be odd and other even
So either b is odd or a is odd, but both of them are not odd and not even
b=8 a =3 b-a =5 is odd a-3b =3-24 = -21 Not even
b=5 a=8 b-a =-3 is odd a-3b = 8-15 = -7 Not even
b=5 a=0 b-a =5 is odd a-3b = -15 Not even
b=0 a=7 b-a =-7 is odd a-3b = 7 Not even
b=7 a=-4 b-a =11 is odd a-3b =-4-21 =-25 Not even
Looks like B or D is the answer
b=3a+3
Substitute b in a -3b=a-3(3a+3)= a-9a-9 = -8a-9
a =-2 -8a-9 = 7 Not even
a =-1 8-9 =-1 Not even
a = 0 0-9 = -9 Not even
a =1 -8-9 =-17 Not even
a=2 -16-9 = -25 Not even
We can definitively say that a-3b is Not even. we have sufficiency in both cases. Correct me if I went wrong with numbers some where.
Thanks for the good Questions
To solve for A convert it to b-a form
b=3a+3
b-a = 2a+3
or b-a = even+odd = odd
another approach:
b=3(a+1)
if a = even then b=3 x odd=odd
if a = odd then b = 3 x even = even
so one is even the other is odd
b=3a+3
b-a = 2a+3
or b-a = even+odd = odd
another approach:
b=3(a+1)
if a = even then b=3 x odd=odd
if a = odd then b = 3 x even = even
so one is even the other is odd
