高階math-u09-d04
A bag holds 3 red and 2 blue counters. Two are drawn at random without replacement. The probability of two reds is:
A. (3/5) x (2/4)✓ 答案
B. (3/5) x (3/5)
C. (3/5) x (2/5)
D. (3/5) x (4/5)
解說
The first draw being red has probability 3/5. After that there are 2 reds in 4 counters, so the second factor is 2/4. Using 3/5 again would wrongly assume the draws are independent.