First convert the 2 1/2 into eighths to be able to subtract the numbers. That becomes 2 4/8. Next set up the subtraction. 11 1/8 - 2 4/8. Note that 4/8 is bigger than 1/8, meaning we have to borrow 8/8 from 11 making our problem 10 9/8 - 2 4/8. Now we subtract as normal: 10 - 2 = 8; 9/8 - 4/8 = 5/8.
Final answer: 8 5/8 inches
