S and T (GMAT Prep)

[alex.gellatly]

If s and t are two different numbers on the number line, is s+t equal to 0?
1. The distance between s and 0 is the same as the distance between t and 0.
2. 0 is between s and t.

[Anurag@Gurome]

If s and t are two different numbers on the number line, is s+t equal to 0?

1. The distance between s and 0 is the same as the distance between t and 0.
2. 0 is between s and t.

For (s + t) to be equal to zero s must be equal to -t, i.e. s and t must lie on the opposite side of zero on the number line and their distance from zero must be equal.

Statement 1: This is only possible if either s = t or s = -t.
As s and t are different numbers, s cannot be equal to t.
Hence, s = -t

Sufficient

Statement 2: This only means either s or t is negative.

Not sufficient

The correct answer is A.