Question

Difficulty: HardIndependent and Dependent Events

A financial analyst chooses two investment assets at random, one after another without replacement, from a portfolio consisting of 33 technology stocks and 22 utility stocks. The probability of achieving a target return depends on the composition of the selected assets:
- If both selected assets are technology stocks, the probability of achieving the target return is 0.800.80.
- If exactly one selected asset is a technology stock, the probability of achieving the target return is 0.500.50.
- If neither selected asset is a technology stock, the probability of achieving the target return is 0.100.10.

What is the probability, expressed as a decimal, that the analyst achieves the target return?

Answer: 0.55

Answer

The probability that the analyst achieves the target return is 0.55.
To find the overall probability of achieving the target return, calculate the probability of each mutually exclusive composition of assets selected without replacement, and weight each by its conditional probability of success. The probability of selecting two technology stocks is (3/5) * (2/4) = 0.30. The probability of selecting one technology stock and one utility stock in either order is (3/5)*(2/4) + (2/5)*(3/4) = 0.60. The probability of selecting two utility stocks is (2/5) * (1/4) = 0.10. Multiplying each by its respective success rate (0.80, 0.50, and 0.10) yields 0.24 + 0.30 + 0.01 = 0.55.

Step-by-Step Solution

1
Determine the probabilities of the three mutually exclusive selection scenarios without replacement.
P(TT) = 0.30, P(1T) = 0.60, P(UU) = 0.10.
Since selections are made without replacement, the outcome of the first draw affects the total count and available assets for the second draw.
2
Calculate the joint probability of achieving the target return for each scenario.
P(TT and Target) = 0.24, P(1T and Target) = 0.30, P(UU and Target) = 0.01.
Multiply the probability of drawing each combination by the conditional probability of success for that specific combination.
3
Sum the joint probabilities across all possible scenarios.
Total Probability = 0.24 + 0.30 + 0.01 = 0.55.
The scenarios are mutually exclusive and exhaustive, so their sum gives the total overall probability of achieving the target return.

Key Concept

Probability of Dependent Events and Law of Total Probability
Estimated Time:2m 0s
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