2)
\frac{5a}{8y} \times \frac{7}{10} = \frac{35a}{80y} = \frac{7a}{16y} .
3)
\frac{ {b}^{2} }{10} \times \frac{5}{b} = \frac{ {5b}^{2} }{10b} = \frac{b}{2} .
4)
\frac{12 {x}^{5} }{25} \times \frac{15}{8 {x}^{2} } = \frac{180 {x}^{5} }{200 {x}^{2} } = \frac{9 {x}^{3} }{10} .
5)
\frac{5}{3a} \times \frac{2b}{3} = \frac{10b}{9a} = 1 \frac{1}{9} ab.
6)
\frac{3x}{4} \times \frac{1}{x} = \frac{3x}{4x} = \frac{3}{4} .