F.3 Math quickly (10marks)

let the student who wear glasses to be A, who doesn't wear glasses to B
Student 1 student 2
A - A/A/A/B/B 2
A - A/A/A/B/B 2
A - A/A/A/B/B 2
B - A/A/A/B/B 3
B - A/A/A/B/B 3

P(only 1 wears glasses)
=12/25

you can use tree diagram to solve the question.

2009-08-02 12:28:38 補充：
oh sorry, 我計錯數, 以下才是正確答案 :
let the student who wear glasses to be A, who doesn't wear glasses to B

2009-08-02 12:28:54 補充：
Student 1 - student 2
A - A/A/B/B - AA / AA / AB / AB (2)
A - A/A/B/B - AA / AA / AB / AB (2)
A - A/A/B/B - AA / AA / AB / AB (2)
B - A/A/A/B - BA / BA / BA / BB (3)
B - A/A/A/B - BA / BA / BA / BB (3)

P(only 1 wears glasses)
=12/16
=3/4
you can use tree diagram to solve the question.

2009-08-02 12:35:29 補充：
~~~~~~~~oh sorry, 我又計錯數, 以下才是正確答案 :~~~~~~~~~~~~~

2009-08-02 12:36:09 補充：
let the student who wear glasses to be A, who doesn't wear glasses to B
Student 1 - student 2
A - A/A/B/B - AA / AA / AB / AB (2)
A - A/A/B/B - AA / AA / AB / AB (2)
A - A/A/B/B - AA / AA / AB / AB (2)
B - A/A/A/B - BA / BA / BA / BB (3)
B - A/A/A/B - BA / BA / BA / BB (3)

2009-08-02 12:36:19 補充：
P(only 1 wears glasses)=12/20=3/5
you can use tree diagram to solve the question.

2 possible situation
1st yes, 2nd no OR
1st no, 2nd yes

SO... probability = 2/5*3/4 + 3/5*2/4 = 12/20 = 3/5

For only 1 wears glasses, it could be :
(1) 1st one with glasses AND 2nd one no glasses. OR
(2) 1st one no glasses AND 2nd one with glasses.
Probability for (1) = (2/5) x [3/(5 - 1)] = (2/5) x (3/4) = 3/10.
Probability for (2) = (3/5) x [2/(5 - 1)] = (3/5) x (2/4) = 3/10.
So probability = (1) + (2) = 3/5.