three and one fourth minus one half

3 1/4 = 13/4 

1/2    =  2/4

 

13/4 - 2/4 = 11/4 or 2 3/4

3 and 1/4 would become 13/4 since 3 times the denominator, 4, is 12, and that plus the current numerator, 1, is 13, becoming the new numerator.

Converting 1/2 into 4ths is 2/4, and 13-2 (the numerators of the numbers) is 11. That means that 3 and 1/4 minus 1/2 is 11/4, or 2 3/4.