Question

A bag contains 9 counters. n counters are yellow and the rest are blue. Two counters are removed randomly from the bag. The probability of the first counter being yellow and the second being blue is 5/18.
Form an equation involving n and show that it simplifies to n^2 - 9n + 20 = 0

Show all working!

Answer 1

Given:
Total counters = 9
yellow =n counters
blue = 9-n

[P(yellow) = n/9 AND P(blue)] =P(y∩b)=(n/9) x (9-n)/8 (8,because 1 yellow already withdrawn)
The equation P(y∩b) =5/18 (Given)

or (n/9) x (9-n)/8 = 5/18
Reducing same denominator (72)

 [n(9-n)/72] = 20/72
Expanding ===> n²-9n+20 =0

Answer 2

>>>>>>>>>>> 0 is the answer <<<<<<<<<<<<