Gary is 8 3/4 years old. His brother is 3 7/12 years younger than he is. How many years old is Gary’s brother?
To add the mixed numbers, convert them to improper fractions: 8 3/4 = (4*8+3)/4 = 35/4, and 3 7/12 = (12*3+7)/12 = 43/12.
His brother is 35/4 - 43/12 = 105/12 - 43/12 = <<105/12-43/12=62/12=31/6>>31/6 years younger than Gary.
So, Gary's brother is 8 3/4 - 31/6 = (4*8+3)/4 - 31/6 = 35/4 - 31/6 = (35*3-31*2)/(4*3) = 105-62/12 = <<105-62/12=43/12=3 7/12>>3 7/12 years old. Answer: \boxed{3\frac{7}{12}}.