1/50-1)(1/49-1)(1/48-1).(1/4-1)(1/3-1)(1/2-1)= (-1)^49 * (1-1/50)(1-1/49)...(1-1/2)= (-1) * (49/50)(48/49)...(2/3)(1/2)= (-1) * (49*48*.*2*1)/(50*49*48*.*3*2)= (-1) * (1)/(50)= -1/50