Ответ:

5×4×3×2×1 120 1

- --------------- = ------ = ---

8×5×4×3×2 960 8

7×6×5×4 840 1 8 9 3

------------ + ⅔ = ------- + ⅔ = ----- + --- = ---- = ---

12×7×6×5 2520 12 12 12 4

11×10×9 7×6 4 990 42 4

- ---------- + ------ + ---- = - ------- + ----- + ---- =

15×11×10 9×7 15 1650 63 15

3 2 4 9 10 4 5

- --- + --- + ----- = - ---- + ----- + ----- = ---- = ⅓

5 3 15 15 15 15 15