Need help with Maths homework
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Need help with Maths homework

[From: ] [author: ] [Date: 11-10-08] [Hit: ]
John will take a ball from the bag. He will look at its colour and then put it back.1) write an expression, in temrs of n, for the probability that john will take a white ball.2) bill states that the probability that john will take a white ball is 2/5.......
Here's the question -

A bag contains (n=7) balls. n are yellow, 7 are white. John will take a ball from the bag. He will look at its colour and then put it back.

1) write an expression, in temrs of n, for the probability that john will take a white ball.

2) bill states that the probability that john will take a white ball is 2/5. Prove this is not correct.

Please help! Thanks.

-
1.
7/(n+7)

2
7/(n+7)=2/5
cross multiplying
35=2n+14
2n=21
n=21/2, but n cannot be a fraction, so he's wrong

-
1. probability of taking a white ball = number of white ball / total balls

= 7 / (n+7)

2. if 7 / (n+7) = 2/5
35 = 2(n + 7)
n =35/2 - 7 which is a fraction...
so 2/5 is not correct.
1
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