Is x less than y?
(1) Sufficient. After some manipulation, we arrive at the inequality x+1<y. If y is bigger than x+1 (a number bigger than x), then it also holds that y is bigger than x.
(2) Insufficient. The inequality can also be stated as x<y+1. Y could very well be bigger than x, but it's also possible that y is not bigger. We are not sure what role the additional 1 plays in this inequality. For instance, in the inequality 10< 25+1, the "+1" doesn't matter. Y is still bigger than x. However, if 2.5<2+1, we see that "+1" determines the direction of the inequality sign and that y is actually smaller than x.
Hence, A is correct.
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