Question

3/4-1,75; 2/3+0,75; 3/7-0,8; 0,04+9/16 !

Answer 1

1) 3/4 -1,75 =3/4 -175/100 =3/4 - 1 3/4 = -1.
2)  2/3 + 0,75 = 2/3 +75/100 =2/3 +3/4 =(4*2+3*3)/12 = 17/12 = 1 5/12.
3)  3/7 -0,8 = 3/7 - 8/10 = (3*10 - 7*8)/70 =(30-56)/70 = -26/70 = -13/35.
4) 0,04+9/16 = 4/100+9/16 =(4*4+ 25*9)/400= (16+225)/400= 241/400. 

Answer 2

$\frac{3}{4} - 1.75 = 0.75 - 1.75 = - 1$ ;

$\frac{2}{3} + \frac{3}{4} = \frac{8}{12} + \frac{9}{12} = \frac{17}{12} = \frac{12+5}{12} = \frac{12}{12} + \frac{5}{12} = 1 \frac{5}{12}$ ;

$\frac{3}{7} - 0.8 = \frac{3}{7} - \frac{8}{10} = \frac{3}{7} - \frac{4}{5} = \frac{15}{35} - \frac{28}{35} = - \frac{13}{35}$ ;

$0.04 + \frac{9}{16} = \frac{4}{100} + \frac{9}{16} = \frac{1}{25} + \frac{9}{16} = \frac{16}{400} + \frac{225}{400} = \frac{241}{400} .$