a: 1/2-1/3=1/6
b: 1/5-1/6=1/30
c: 1/3-1/4=1/12
d: 1/7-1/8=1/56
\(\dfrac{1}{2}-\dfrac{1}{3}=\dfrac{3}{6}-\dfrac{2}{6}=\dfrac{1}{6}\)
\(\dfrac{1}{5}-\dfrac{1}{6}=\dfrac{6}{30}-\dfrac{5}{30}=\dfrac{1}{30}\)
\(\dfrac{1}{3}-\dfrac{1}{4}=\dfrac{4}{12}-\dfrac{3}{12}=\dfrac{1}{12}\)
\(\dfrac{1}{7}-\dfrac{1}{8}=\dfrac{8}{56}-\dfrac{7}{56}=\dfrac{1}{56}\)