11/8 - 5/4 ...Find the LCD and this LCD can be divided by the two denominators.
= 1 * 11 /8 - 2 * 5/ 8 -----8 is the LCD; we divide 8 to the first denominator and multiply to its numerator and copy the operation ,the same process to the second fraction
= 11/8 - 10/8
= 1/8 is the final answer