490. 1) (7/5 - 1) : (1 - 7/10 * 3/5) 2) (8/15 - 3/4 + 2/5 - 8/60) : (4/7 - 1/3) 3) (1/13 * 1/42 + 5/7) : (8/21 : (8/1 + 3/2)) 4) 2 5/15 : 6/15 + 1/14 - 1/73 * (5/7 - 1/16)

Решение:

1)

(7/5 - 1) : (1 - 7/10 * 3/5)

1. (7/5 - 5/5) = 2/5
2. (7/10 * 3/5) = 21/50
3. (1 - 21/50) = 29/50
4. (2/5) : (29/50) = 2/5 * 50/29 = 20/29

2)

(8/15 - 3/4 + 2/5 - 8/60) : (4/7 - 1/3)

1. 8/60 = 2/15
2. 8/15 - 3/4 + 2/5 - 2/15 = 6/15 - 3/4 + 2/5 = 2/5 - 3/4 + 2/5 = 4/5 - 3/4 = (16 - 15)/20 = 1/20
3. (4/7 - 1/3) = (12 - 7)/21 = 5/21
4. (1/20) : (5/21) = 1/20 * 21/5 = 21/100

3)

(1/13 * 1/42 + 5/7) : (8/21 : (8/1 + 3/2))

1. 1/13 * 1/42 = 1/546
2. 1/546 + 5/7 = (1 + 390)/546 = 391/546
3. 8/1 + 3/2 = (16 + 3)/2 = 19/2
4. 8/21 : 19/2 = 8/21 * 2/19 = 16/399
5. 391/546 : 16/399 = 391/546 * 399/16 = (13*30 + 1)/546 * 399/16 = (17*23) / (14*39) * (3*7*19) / 16 = 17/42 * 19/8 = 323/336

4)

2 5/15 : 6/15 + 1/14 - 1/73 * (5/7 - 1/16)

1. 2 5/15 = 35/15 = 7/3
2. 7/3 : 6/15 = 7/3 * 15/6 = 35/6
3. 5/7 - 1/16 = (80 - 7)/112 = 73/112
4. 1/73 * 73/112 = 1/112
5. 35/6 + 1/14 - 1/112 = (1960 + 8 - 7) / 112 = 1961/112

Ответ:

1) 20/29
2) 21/100
3) 323/336
4) 1961/112