Am not sure if there's a difference but I would solve them with using lcm method.
With the first question it can be easily determine as 2 is a factor of 4 however in the second question the lcm is found by multiplying the denominator.
[tex] \frac{1}{2} + \frac{1}{4} \\ the \: lcm \: is \: 4\: \\ \frac{1 \times 2}{4} + \frac{1 \times 1}{4} = \frac{3}{4} [/tex]
[tex] \frac{1}{2} + \frac{1}{3} \\ The \: lcm \: is \: 6 \\ \frac{1 \times 3}{6} + \frac{1 \times 2}{6} = \frac{5}{6} [/tex]
