A bag has 3 red and 5 blue marbles, P(red) Step by Step

Step by step

The question

Question: A bag has 3 red and 5 blue marbles.

One marble is picked without looking.

What is the probability it is red?

The probability is a fraction: the outcomes we want, over all the outcomes.

P(red) = we wantall

P stands for probability.

P = probability

1 Count all outcomes

So there are 8 marbles in all.

all = 8

3 plus 5 is 8.

3 + 5 = 8

2 Count the ones we want

The red marbles: 3.

That is 3 outcomes we want.

we want = 3

3 Write the fraction

3 we want, out of 8.

So the probability is 3/8.

P(red) = 38

Careful!

The bottom is all the outcomes, 8.

Not only the other 5.

Careful: not 35 ✗

4 As a percent

Percent means out of 100.

3/8 means 3 divided by 8.

Then times 100.

To the nearest tenth, that is about 37.5%.

P(red) ≈ 37.5%

3 ÷ 8 = 0.375…

0.375… × 100 ≈ 37.5%

5 Check

Let's check with the others.

8 minus 3 is 5.

3/8 plus 5/8 is 8/8: that is 1, all of them.

So the answer is right!

P(red) + P(not red) = 38 + 58 = 88 = 1

Let's look back.

First: count all outcomes.

Then: count the ones we want.

Then: write the fraction.

Then: as a percent.

Last: check.

Answer