Bjr,
1/3 + (2/5 + 4/7 - 1/3) - (2/5 + 3/2) =
70/120 + (84/210 + 120/210 - 70/210) - (84/210 + 315/210) =
70/120 + 134/210 - 399/210 = -195/210 = - (15 * 13)/(15 * 14) = -13/14.
