1/15+1/14*15+1/13*14+1/12*13+1/11*12

1/15 + 1/14 * 15 + 1/13 * 14 + 1/12 * 13 + 1/11 * 12 = 4 7793/20020.

1. 1/14 * 15 = 15/14.

2. 1/13 * 14 = 14/13.

3. 1/12 * 13 = 13/12.

4. 1/11 * 12 = 12/11.

5. 1/15 + 15/14 = (14 + 225) / 210 = 239/210.

6. 239/210 + 14/13 = (3107 + 2940) / 2730 = 6047/2730.

7. 6047/2730 + 13/12 = (12094 + 5915) / 5460 = 18009/5460 сократим на 3 = 6003/1820.

8. 6003/1820 + 12/11 = (66033 + 21840) / 20020 = 87873/20020 = 4 7793/20020.