F.5 MATHS probability

yan

2010-12-15 2:53 pm

1. There are 3 boxes on the table. Each box contains some balls as shown:Box A : 2 table tennis and 1 tennisBox B : 1 table tennis and 1 golfBox C : 3 tennis(a) If one selects one of the boxes and picks up a ball randomly, write down an impossible event.(b) Winnie selects one of the boxes and she picks up a ball randomly. What is the probability that she(i) gets a golf;(ii) gets a table tennis.(c) Both Victor and Winnie choose a box and pick up a ball with replacement randomly. Find the probability that both of them select a tennis from the same box.

回答 (1)

用戶25975

2010-12-15 3:42 pm

✔ 最佳答案

a) Impossible event: Box C and a golf is selected

b i) Only 1 possibility: Box B and golf, prob. = 1/3 x 1/2 = 1/6

ii) Possiblilities: Box A and table tenis, prob. = 1/3 x 2/3 = 2/9

Box B and table tennis, prob. = 1/3 x 1/2 = 1/6

Total prob. = 2/9 + 1/6 = 7/18

c) Each trial, possibilities to get tennis are:

Box A and tennis, prob. = 1/3 x 1/3 = 1/9

Box B and tennis, prob. = 1/3 x 1/2 = 1/6

Box C and tennis, prob. = 1/3 x 1 = 1

So total prob. = 1/9 + 1/6 + 1 = 13/18

P(Both gets tennis) = 13/18 x 13/18 = 169/324

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