[tex]1\frac{1}{4}=a+\frac{3}{8}[/tex]
First, express the mixed number as a simple fraction:
[tex]1\text{ }\frac{1}{4}=\frac{(1\cdot4+1)}{4}=\frac{5}{4}[/tex]
Back with the equation:
[tex]\frac{5}{4}=a+\frac{3}{8}[/tex]
Subtract 3/8 from both sides of the equation:
[tex]\frac{5}{4}-\frac{3}{8}=a+\frac{3}{8}-\frac{3}{8}[/tex][tex]\frac{10}{8}-\frac{3}{8}=a[/tex]
