A bag contains 16 red balls and 20 blue balls only. How many white balls must be added to the bag so that the probability of randomly picking a red ball is equal to \(\frac{2}{5}\)
-
4
- 20
- 24
- 40
The correct answer is: A
Explanation
Number of red balls = 16,
Number of blue balls = 20
Let x represent the No of white balls to be added
∴ Total number of balls = 36 + x
Pr( red ball) = \(\frac{ 16}{ 36 + x } = \frac{2}{5}\) (remember that Pr( red ball ) = \frac{2}{5}\))
cross multiplying
2(36 + x) = 80
2x = 80 - 72
2x = 8
x = \(\frac{8}{2}\)
= 4