http://www.litecoinpool.org/calc?hashrate=425&difficulty=205.77652398

This is an estimate of what you could be getting in a pool vs. expected probabilities of finding a block. I found the hashrate of 425 over here: https://github.com/litecoin-project/litecoin/wiki/Mining-hardware-comparison

I am afraid your 280 is slower than it should be.

Looking at the numbers, it will take you almost a month to get the reward of 25 coins, $4 and change each, versus $260 a month in a pool.