5/10-4/25;
45/100-17/50;
75/100-1/5;
2/5-15/100

$frac{5}{10} - frac{4}{25} = frac{5*10}{10*10} - frac{4*4}{25*4} = frac{50}{100} - frac{16}{100} = frac{50-16}{100} = frac{34}{100} =0,34$

$frac{45}{100} - frac{17}{50} = frac{45}{100} - frac{34}{100}= frac{11}{100} =0,11$

$frac{75}{100} - frac{1}{5} = frac{75}{100} - frac{20}{100} = frac{55}{100} =0,55$

$frac{2}{5} - frac{15}{100} = frac{40}{100} - frac{15}{100} = frac{25}{100} =0,25$