In a supermarket lucky draw, a participant will first spin a wheel, followed by throwing a fair six-sided die. The wheel has 9 sections and an arrow which has an equal chance of coming to rest over any of the 9 sections. The wheel has one section labelled "4" and five sections labelled "". The fair six-sided die has two faces labelled "0.02", three faces labelled "0.5" and one face labelled "2". The amount of money that the participant wins is calculated by taking the multiplication of the outcomes of the wheel and die.
- (a)
Find the probability that a participant wins $2.
- (b)
If a participant wins 100$.
- (c)
A participant plays three consecutive lucky draws. Find the probability that a participant wins $6 in total, such that the die shows a different face value each time.
- (d)
Another participant plays one lucky draw. He is now given an option to either end the game by taking the amount based on the section that the wheel came to rest over, or to proceed to throw the die. Explain, with justification, which option should he take.
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Worked solution
7(a)
1. Identify all the combinations of wheel and die outcomes that result in a $2 win.
The possible (wheel, die) combinations that multiply to $2 are:
- since
- since
- since
2. Calculate the probability for each combination and sum them to find the total probability.
7(b)
1. Retrieve or calculate the total probability of winning $2 from part (a).
From part (a), the probability of winning $2 is the sum of probabilities of the mutually exclusive winning combinations:
2. Calculate the probability that the participant lands on $100 AND wins $2.
The only way to win $2 when the wheel lands on $100 is for the die to show 0.02.
3. Apply the conditional probability formula to find the required probability.
Using the concept of conditional probability:
7(c)
1. Deduce the exact sequence of winnings required to win $6 with three different die face values.
Let the three different die face values rolled be , , and .
Let the corresponding wheel values landed on be .
Total winnings
Since , if , the total will exceed . Thus, we must have .
This leaves .
If , the sum exceeds . If , we get (impossible since the maximum wheel value is ).
Thus, must be , giving . This implies .
Therefore, the only way to satisfy the conditions is to win exactly in each of the three draws via these specific combinations:
- Wheel and Die
- Wheel and Die
- Wheel and Die
2. Calculate the total probability by considering the permutations of the three specific events.
Calculate the probability of each specific combination occurring in a single draw:
Since the participant plays three consecutive draws, these 3 distinct events can occur in any order. The number of possible arrangements is .
7(d)
1. Calculate the expected value (average) of the multiplier from throwing the die.
2. Compare the expected multiplier with 1 to justify the decision.
Since the expected multiplier is less than , throwing the die will, on average, decrease the final prize money regardless of what section the wheel came to rest over.
Therefore, he should choose to end the game and take the amount based on the wheel.
He should choose to end the game, as the expected multiplier from throwing the die is (which is less than ). Thus, throwing the die will decrease his expected prize.
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