To find the difference of 21-15/16 and 18-3/4, we need to subtract the second number from the first:
21-15/16 - 18-3/4
To subtract fractions, we need a common denominator. The least common multiple of 16 and 4 is 16, so we will convert both fractions to have a denominator of 16:
21 - (15/16) - 18 + (12/16)
Now we can combine the whole numbers and the fractions separately:
21 - 18 = 3
and
-15/16 + 12/16 = -3/16
Putting the whole thing together, we get:
3 - 3/16
This is the difference of the two numbers in mixed number form. If we want to express the answer as an improper fraction, we need to multiply the whole number by the denominator and add the numerator:
3 x 16 + (-3) = 45
So the difference is:
45/16