`a)10/16 : 4/21`
`=105/32`
`=105:32`
`b)1,3:2,75`
`=26/55`
`=26:55`
`c)[-2]/5:0,25`
`=[-8]/5`
`=-8:5`
`a,` \(\dfrac{10}{16}\div\dfrac{4}{21}=\dfrac{5}{8}\div\dfrac{4}{21}=\dfrac{105}{32}=105\div32\)
`b,` \(1,3\div2,75=\dfrac{13}{10}\div\dfrac{11}{4}=\dfrac{26}{55}=26\div55\)
`c,` \(-\dfrac{2}{5}\div0,25=-\dfrac{2}{5}\div\dfrac{1}{4}=-\dfrac{8}{5}=-8\div5\)