Determine how many red balls are in the box, using the following information.
A box has blue and red balls. If there are 20 blue balls, the probability of picking a red ball when a ball is picked at random is 4/6.
Let the number of red balls be x.
So the total number of balls is x+20.
Now the probability that a ball picked at random is red is 20/(x+20)
As the probability is given as 4/6
=> x / (x + 20) = 4/6
=> 6x = 4x + 80
=> 6x - 4x = 80
=> 2x = 80
=> x = 80/2
=> x = 40.
Therefore there are 40 red balls in the box.
The probability is the ratio between the number of possible events and the total number of events.
P = the number of possible events/total number of events
Let's put the number of blue balls as b and the number of red balls as a.
But b = 20
The total number of balls is: a+b = a + 20
Let's consider the balls as being the events. The posisbility of picking a red ball is a.
P = a/(a+20)
But P = 4/6
P = 2/3
2/3 = a/(a+20)
We'll cross multiply and w'ell get:
3a = 2a + 40
a = 40
The number of red balls from the box is a = 40 red balls.