, решить уравнения и сделать к ним проверку: -1,2x=6,6;
-4,3x=14,62;
-5,4y=-32,94;
1,7a+2=1,7-0,3a.

1)(16 3/5+17 7/10)-(25 5/8-18 3/4)=27 17/40
16 3/5+17 7/10=16 6/10+17 7/10=33 13/10=34 3/10
25 5/8-18 3/4=25 5/8-18 6/8=7 5/8-6/8=7-1/8=6 7/8
34 3/10-6 7/8=34 12/40-6 35/40=28 12/40-35/40=28-23/40=27 17/40

2)4 2/5-(8 7/60+3 3/4-8 7/15)=1
8 7/60+3 3/4-8 7/15=8 7/60+3 45/60-8 28/60=3 24/60=3 2/5
4 2/5-3 2/5=1

3)25 7/9-8 3/4-(13 5 /12+2 11/18)=1
13 5 /12+2 11/18=13 15 /36+2 22/36=15 37/36=16 1/36
25 7/9-8 3/4-16 1/36=25 28/36-8 27/36-16 1/36=1 

4)(20-19 3/4)+(17 3/4-17)+(2 1/2-17/24)=здесь проще открыть скобки и решить прямо
=20-19 3/4+17 3/4-17+(2 1/2-17/24)=(20-17)+(-19 3/4+17 3/4)+(2 1/2-17/24)=
=3-2+(2 12/24-17/24)=1+(2 -5/24)=1+1 19/24=2 19/24

1) -5 × 49 × 4 = (-5 × 4) × 49 = -20 × 49 = -980.

2) 3 1/8 (-y + 8) - 4 5/8 (y - 16) = ((3 1/8 × (-y)) + (3 1/8 × 8)) - ((4 5/8 × y) + (-4 5/8 × 16)) = (3 1/8 y + 25/8 × 8) - (4 5/8 y - 37/8 × 16) = 3 1/8 y + 25 - 4 5/8 y - 74

= -1 1/2 - 49 = -1 1/2 - 48 2/2 = - (1 1/2 + 48 2/2) = - 49 3/2 = -50 1/2.

3) 0,8 × (-125) × 0,5 × (-2) = -100 × (-1) = 100.

4) -3,73 × 50 × (-2) × (-0,01) = (50 × (-2) × (-0,01)) × (-3,73) = 1 × (-3,73) = -3,73.

5) 7/8 × (-4,5) × (-1 1/7) × 0,4 = 7/8 × 9/2 × 8/7 × 2/5 = 7 × 9 × 8 × 2/8 × 2 × 7 × 5 = 1 × 9 × 1 × 1/1 × 1 × 1 × 5 = 9/7 = 1 2/7.

6) -4/9 × (-3/11) × 9,16 × (-22) = - (4/9 × 3/11 × 22) × 9,16 = -8/3 × 9 4/25 = -1832/75 = -24 32/75.

ответ: 1) -980;

2) -50 1/2;

3) 100;

4) -3,73;

5) 1 2/7;

6) -24 32/75.

Удачи Вам всегда и во всём! :)