395. A box contains 100 balls, numbered from 1 to 100. If three balls are selected at random and with replacement from the box, what is the probability that the sum of the three numbers on the balls selected from the box will be odd? A) 1/4; B) 3/8; C) 1/2; D) 5/8; E) 3/4 我选A，这3个数要和为奇有2种可能 - 奇奇奇、2偶1奇（没顺序）。每种可能(1/2)*(1/2)*(1/2) = 1/8，总共(1/8)*2 = 1/4。 但答案是C，这3个数要和为奇有4种可能 - 奇奇奇、偶偶奇、奇偶偶、偶奇偶（有顺序）。每种可能(1/2)*(1/2)*(1/2) = 1/8，总共(1/8)*4 = 1/2。 请问为什么算和sum, 要考虑顺序呢？ | 
