$\displaystyle \frac{3a+1}{a+b}$\displaystyle \frac{3a+1}{a+b}

$\displaystyle \frac{2a+1}{a+b}$\displaystyle \frac{2a+1}{a+b}

$\displaystyle \frac{2a+1}{a+2b}$\displaystyle \frac{2a+1}{a+2b}

$\displaystyle \frac{3a+1}{2b+a}$\displaystyle \frac{3a+1}{2b+a}