chetan2u wrote:

Is a-3b an even number?

1). b=3a+3

2). b-a is an odd number

for a -3b to equal even then a and b must be even or odd. One cannot be even and the other odd

Example:

if b = 3 to get an even a can be 11 but not 12

if b = 2 to get an even a must be even

1) b = 3a + 3

b = 3(a + 1)

if a = 2 then b = 9

if a = 3 then b = 12

none are both even or none are both odd so you can answer the question

2. b -a = odd

to get an odd b and a must be different

answer is D, each on its own that neither one will result in an even