A bag contains (n + 7) tennis balls.
n of the balls are yellow.
The other 7 balls are white.
John will take at random a ball from the bag.
He will look at its colour and then put it back in the bag.
(b) (i) Write down an expression, in terms of n, for the probability that John will take a white ball.
Bill states that the probability that John will take a white ball is 2/5
(ii) Prove that Bill’s statement cannot be correct.
After John has put the ball back into the bag, Mary will then take at random a ball from
the bag.
She will note its colour.
(c) Given that the probability that John and Mary will take balls with different
colours is 4/9
prove that 2n^2– 35n + 98 = 0