\(a,\dfrac{5\times7\times8\times9\times10}{7\times8\times9\times10\times11}\) \(=\dfrac{5}{11}.\)
\(b,\dfrac{3\times145+3\times55}{6\times215+6\times85}\\ =\dfrac{3\times\left(145+55\right)}{6\times\left(215+85\right)}\\ =\dfrac{145+55}{2\times\left(215+85\right)}\\ =\dfrac{200}{2\times300}\\ =\dfrac{2\times100}{2\times3\times100}\\ =\dfrac{1}{3}.\)
b,\(=\dfrac{3\times\left(145+55\right)}{6\times\left(215+85\right)}=\dfrac{3\times200}{6\times300}=\dfrac{3}{6}\times\dfrac{2}{3}=\dfrac{6}{18}\)
a)\(\dfrac{1}{11}\)
b)\(\dfrac{1}{6}\)
