If x-y=8, which of the following must be true?
I. Both x and y are positive
II. If x is negative, y must be negative
III.If x is positive, y must be positive Select the correct option:
A) I only
B) II only
C) III only
D) I and II
E) II and III
The best way to approach such questions is to plug in values for x and y   Given: x-y=8   I. Both x and y are positive:   Let x=10 and y=2   x-y=8   But,   Let x=6 and y=-2   x-y=8   Therefore, NOT TRUE   III. If x is positive, y must be positive   Let x=10 and y=2   x-y=8   But,   Let x = 6 and y=-2   x-y=8   Therefore, NOT TRUE   II. If x is negative, y must be negative   If x is negative, for the expression x-y=8 to be true, y must be a -ve number. Otherwise, the sum of two negative numbers will yield another negative number!   Therefore, TRUE   Ans: 'II only'
<result>B</result>
If x-y=8, which of the following must be true?
I. Both x and y are positive
II. If x is negative, y must be negative
III.If x is positive, y must be positive