In a game two dice are used.
Die A has 2 blue faces and 4 yellow faces.
Die B has 4 blue faces and 2 pink faces.
The two dice are thrown together.

  1. (i)

    Find the probability that

    1. (a)

      both dice show a blue face on top.

      Answer ...

    2. (b)

      just one die shows a blue face on top.

      Answer ...

  2. (ii)

    If both dice show blue, the player wins a prize.
    If just one show blue, the player throws both dice again.
    He also wins a prize if both show blue on the second throw.
    Calculate the probability that the player wins a prize on either the first throw or second throw.

    Answer ...

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Worked solution

b(i)(a)

1. Calculate the probability that both dice show blue

P(A blue)=26=13,P(B blue)=46=23P(\text{A blue})=\frac{2}{6}=\frac{1}{3},\qquad P(\text{B blue})=\frac{4}{6}=\frac{2}{3}

Since both dice must show blue,
P(both blue)=13×23=29.P(\text{both blue})=\frac{1}{3}\times\frac{2}{3}=\frac{2}{9}.

Answer

29\dfrac{2}{9}

b(i)(b)

1. Identify the two ways that just one die can show blue

Just one blue means either:

AA is blue and BB is not blue, or AA is not blue and BB is blue.

P(A blue)=26=13P(A\text{ blue})=\dfrac{2}{6}=\dfrac{1}{3}, P(A not blue)=46=23P(A\text{ not blue})=\dfrac{4}{6}=\dfrac{2}{3}

P(B blue)=46=23P(B\text{ blue})=\dfrac{4}{6}=\dfrac{2}{3}, P(B not blue)=26=13P(B\text{ not blue})=\dfrac{2}{6}=\dfrac{1}{3}

2. Calculate and add the probabilities of the two mutually exclusive cases

P(just one blue)=(13×13)+(23×23)P(\text{just one blue})=\left(\dfrac{1}{3}\times\dfrac{1}{3}\right)+\left(\dfrac{2}{3}\times\dfrac{2}{3}\right)

=19+49=59=\dfrac{1}{9}+\dfrac{4}{9}=\dfrac{5}{9}

Answer

49\dfrac{4}{9}

b(ii)

1. Identify the probabilities needed from the first throw and second throw

From earlier parts,

P(both blue)=29P(\text{both blue})=\dfrac{2}{9}

P(just one blue)=49P(\text{just one blue})=\dfrac{4}{9}

For a new throw, the probability of both blue is still 29\dfrac{2}{9}.

2. Calculate the probability of winning on the second throw after just one blue on the first throw

P(just one blue first, then both blue second)=49×29=881P(\text{just one blue first, then both blue second})=\frac{4}{9}\times\frac{2}{9}=\frac{8}{81}

3. Add the mutually exclusive winning probabilities

P(wins)=P(both blue first)+P(just one blue first, then both blue second)P(\text{wins})=P(\text{both blue first})+P(\text{just one blue first, then both blue second})

=29+881=\frac{2}{9}+\frac{8}{81}

=1881+881=2681=\frac{18}{81}+\frac{8}{81}=\frac{26}{81}

Answer

2681\dfrac{26}{81}

AI analysis — may contain mistakes.

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