1 − 2 + 3 / 4 / 5 + 6 / 7 / 8 / 9 / 10 − 11 + 12 − 13 / 14 / 15 = 15 / 12 / 14 Some analysis: 1−2 + (3/4/5) + (6/7/8/9/10) −11+12 − (13/14/15) = 15/12/14 −1 + 3/20 + 6/5040 +1 − 13/210 = 15/168 3/20 + 6/5040 − 13/210 = 15/168 126/840 + 1/840 − 52/840 = 75/840