Ответ:

12/13 · 3/8 = 12 · 3 / 13 · 8 = 3 · 3 / 13 · 2 = 9/26 = 3/12 = 1/4 = 0.25

1. 5/6 · 9/11 = 5 · 9 / 6 · 11 = 5 · 3 / 2 · 11 = 15/22;

2. 5/4 · 7/10 = 5 · 7 / 4 · 10 = 1 · 7 / 4 · 2 = 7/8;

3. 6/7 · 14/11 = 6 · 14 / 7 · 11 = 6 · 2 / 1 · 11 = 12/11 = 1 1/11;

4. 51/61 · 5/17 = 51 · 5 / 61 · 17 = 3 · 5 / 61 · 1 = 15/61;

1. 11/12 · 21/22 = 11 · 21 / 12 · 22 = 1 · 7 / 4 · 2 = 7/8;

2. 8/9 · 7/16 = 8 · 7 / 9 · 16 = 1 · 7 / 9 · 2 = 7/18;

3. 25/27 · 18/35 = 25 · 18 / 27 · 35 = 5 · 2 / 3 · 7 = 10/21;

4. 15/16 · 4/5 = 15 · 4 / 16 · 5 = 3 · 2 / 4 · 1 = 3 · 1 / 2 · 1 = 3/2 = 0.15;

5. 23/33 · 22/23 = 23 · 22 / 33 · 23 = 1 · 2 / 3 · 1 = 2/3;

1. 1/15 · 4 = 1/15 · 4/1 = 1/15 = 1 · 4 / 15 · 1 = 1/15 = 4/15 = 1/15 = 4 · 1 / 15 = 4/15;

2. 3/7 · 2 = 3/7 = 3/7 · 2/1 = 3/7 = 3 · 2 / 7 · 1 = 3/7 = 6/7 = 3/7 = 6 · 3 / 7 = 18/7 = 2 4/7;

3. 5/9 · 3 = 5/9 = 5/9 · 3/1 = 5/9 = 5 · 3 / 9 · 1 = 5/9 = 5 · 1 / 3 · 1 = 5/9 = 5/3 · 5/9 = 5 · 5 / 3 · 9 = 25/27;

4. 5 · 9/10 = 5/1 · 9/10 = 5 · 9 / 1 · 10 = 1 · 9 / 1 · 2 = 9/2 = 4 1/2 = 22.5;

5. 6 · 7/9 = 6/1 · 7/9 = 6 · 7 / 1 · 9 = 2 · 7 / 1 · 3 = 14/3 = 4 2/3.