Probability Trees Tables

Find the probability of selecting two strawberry sweets

Find P(SL)

Find P(OL)

• 0.9

• 0.09

• 1.0

• 0.81

Keith has 3 coloured balls in a bag- red, blue and yellow.

He picks one, records its colour, puts it back and picks another.

a)Complete the table to show the possible outcomes

• RY BY YB

  RY YR YB

• RB BB YB

  RY BY YY

Keith has 3 coloured balls in a bag- red, blue and yellow.

He picks one, records its colour, puts it back and picks another.

Write down the probability Keith picks:

i) two balls of the same colour

Keith has 3 coloured balls in a bag- red, blue and yellow.

He picks one, records its colour, puts it back and picks another.

Write down the probability Keith picks:

ii) two balls of different colour

Answer explanation

Either they are the same colour or not - same colour 1/3 so not same is 2/3

Keith has 3 coloured balls in a bag- red, blue and yellow.

He picks one, records its colour, puts it back and picks another.

Write down the probability Keith picks:

iii) at least one yellow ball

The Watsons regard one boy and one girl as the ideal family. What is the chance of getting one boy and one girl in their planned family of two?

• 0.25 + 0.25 = 0.5

• 0.5 x 0.5 = 0.25

Answer explanation

The probability of getting one of each is:

P(G,B) + P(G,B) = 0.5 x 0.5 = 0.25 + 0.5 x 0.5 = 0.25 = 0.5 (or 1/2 or 50%)

If I toss a coin twice, what is the probability of getting at least one head?

• 1/4 +1/2 = 3/4

• 1/4 + 1/4 + 1/4 = 3/4

• 1/2 x 1/2 = 1/4

Answer explanation

So the probability of getting at least one head is 1/4 + 1/4 + 1/4 = 3/4. (0.75 or 75%)

The probability tree shows the outcomes of flipping a coin twice.

What is the probability the coin lands on heads twice?

• 0.5

• 0.1

• 0.25

• 1