1) 7-3/5+2 7/9; 2) 5 2/7-1/3+6; 3) 9+1 3/4-2/5; 4) 3

1) 7 - 3/5 + 2 7/9 = 9 8/45;

1-ое действие.

7 - 3/5 = 35/5 / 3/5 = 32/5;

2-ое деянье.

32/5 + 2 7/9 = 32/5 + 25/9 = 288/45 + 125/45 = (288 + 125)/45 = 413/45 = 9 8/45;

2) 5 2/7-1/3+6 = 10 20/21;

а) 5 2/7 - 1/3 = 37/7 - 1/3 = 111/21 - 7/21 = (111 - 7)/21 = 104/21 = 4 20/21;

б) 4 20/21 + 6 = 10 20/21;

3) 9+1 3/4-2/5 = 10 7/20;

а) 9 + 1 3/4 = 10 3/4;

б) 10 3/4 - 2/5 = 43/4 - 2/5 = 215/20 - 8/20 = (215 - 8)/20 = 207/20 = 10 7/20;

4) 3 5/12-4/5+31/60 = 3 2/15;

а) 3 5/12 - 4/5 = 41/12 - 4/5 = 205/60 - 48/60 = (205 - 48)/60 = 157/60 = 2 37/60;

б) 2 37/60 + 31/60 = 157/60 + 31/60 = (157 + 31)/60 = 188/60 = 3 8/60 = 3 2/15;

5) 6 5/9+3-7/1 = 2 5/9;

а) 6 5/9 + 3 = 9 5/9;

б) 9 5/9 -7/1 = 9 5/9 - 7 = 2 5/9;