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...

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.

Asked on by tonys538

2 Answers | Add Yours

justaguide's profile pic

justaguide | College Teacher | (Level 2) Distinguished Educator

Posted on

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.

giorgiana1976's profile pic

giorgiana1976 | College Teacher | (Level 3) Valedictorian

Posted on

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.

Probability is:

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.

We’ve answered 318,990 questions. We can answer yours, too.

Ask a question