5 / 7 + 2 / 7, 1 / 6 + 1 / 6, 4 / 11-4 / 11, 3 / 14 + 5 / 14, 9 / 16-5 / 16 6 / 17 + 3 / 17, 15 / 13-5 / 13

5 / 7 + 2 / 7, 1 / 6 + 1 / 6, 4 / 11-4 / 11, 3 / 14 + 5 / 14, 9 / 16-5 / 16 6 / 17 + 3 / 17, 15 / 13-5 / 13

5 / 7 = 1 / 7
1 / 6 + 1 / 6 = 2 / 6 = 1 / 3
4 / 11-4 / 11 = 0
3 / 14 + 5 / 14 = 8 / 14 = 4 / 7
2 / 5 + 1 / 5 = 3 / 5
9-5 out of 16 = 4 / 16 = 1 / 4
6 out of 17 + 3 out of 17 = 9 / 17
15-5 out of 13 = 10 / 13

1 / 2 * 3 * 4 * 5 + 1 / 3 * 4 * 5 * 6 + 1 / 4 * 5 * 6 * 7 +... + 1 / 13 * 14 * 15 * 16

1 / 2 * 3 * 4 * 5 + 1 / 3 * 4 * 5 * 6 + 1 / 4 * 5 * 6 * 7 +... + 1 / 13 * 14 * 15 * 16
=1/3*（1/2*3*4-1/3*4*5+1/3*4*5-1/4*5**6+1/4*5*6-1/5*6*7+•••••+1/13*14*15-1/14*15*16）
=1/3*（1/2*3*4-1/14*15*16）
=1/3*（1/12-1/3360）
=1/3*279/3360
=279/10080

Eleven out of fifteen times seven times three

1/15*3/7=1/35