8/12 + 9/12 = 17/12
12/15 - 5/15 = 7/15
4 x 8/3 = 32/3
1/8 x 3 = 3/8
5 x 2 = 10
2/5 x 1/4 = 2/20 = 1/10
\(\dfrac{2}{3}+\dfrac{3}{4}=\dfrac{8}{12}+\dfrac{9}{12}=\dfrac{17}{12};\dfrac{4}{5}-\dfrac{1}{3}=\dfrac{12}{15}-\dfrac{5}{15}=\dfrac{7}{15}\\ 4\times\dfrac{8}{3}=\dfrac{32}{3};\dfrac{1}{8}\times3=\dfrac{3}{8}\\ 5:\dfrac{1}{2}=5\times\dfrac{2}{1}=10;\dfrac{2}{5}:4=\dfrac{2}{5}\times\dfrac{1}{4}=\dfrac{2}{20}=\dfrac{1}{10}\)