353
First, add the digits other than the units, 250 + 90 = 340. Remember that for a moment. Now, add the one's digits, 8 + 5 = 13. Now, add the 13 to the 340 to get 353. ---- Alternately, subtract 5 from 258 and give it to 95, so we have 253 + 100 = 353.