Fractions

$$a(b/c) = {ab}/c$$
$$a/b + c/b = {a+c}/b$$
$$a/b - c/b = {a-c}/b$$
$$a/b + c/d = {ad+bc}/{bd}$$
$$a/b - c/d = {ad-bc}/{bd}$$
$$a/b x c/d = {ac}/{bd}$$
$$a/b {÷} c/d = a/b x d/c = {ad}/{bc}$$