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Question

A can hit a target 3 times in 5 shots, B 2 times in 5 shot and C three times in 4 shots. All of them fire one shot each simultaneously at the target. What is the probability that atleast two shots hit?

The correct answer is
$\frac{63}{100}$

Probability Problem Analysis

This problem involves calculating the probability of a specific event occurring when multiple independent events happen simultaneously. We need to determine the likelihood that at least two out of three individuals (A, B, and C) successfully hit the target with their single shots.

Defining Individual Probabilities

First, let's determine the probability of each person hitting the target and the probability of them missing the target. We assume each shot is an independent event.

  • Person A: Hits 3 out of 5 shots.

    Probability of A hitting, $P(A) = \frac{3}{5}$

    Probability of A missing, $P(A') = 1 - P(A) = 1 - \frac{3}{5} = \frac{2}{5}$

  • Person B: Hits 2 out of 5 shots.

    Probability of B hitting, $P(B) = \frac{2}{5}$

    Probability of B missing, $P(B') = 1 - P(B) = 1 - \frac{2}{5} = \frac{3}{5}$

  • Person C: Hits 3 out of 4 shots.

    Probability of C hitting, $P(C) = \frac{3}{4}$

    Probability of C missing, $P(C') = 1 - P(C) = 1 - \frac{3}{4} = \frac{1}{4}$

Calculating Probability of 'At Least Two Shots Hit'

The event 'at least two shots hit' includes the following mutually exclusive scenarios:

  • Exactly two shots hit the target.
  • Exactly three shots hit the target.

We will calculate the probability of each scenario and then sum them up.

Scenario 1: Exactly Two Shots Hit

This scenario can occur in three distinct ways, based on who misses the target:

  • A hits, B hits, C misses: The probability is $P(A \cap B \cap C') = P(A) \times P(B) \times P(C')$
  • A hits, B misses, C hits: The probability is $P(A \cap B' \cap C) = P(A) \times P(B') \times P(C)$
  • A misses, B hits, C hits: The probability is $P(A' \cap B \cap C) = P(A') \times P(B) \times P(C)$

Let's calculate the probability for each specific combination:

  • Probability (A hits, B hits, C misses) = $\frac{3}{5} \times \frac{2}{5} \times \frac{1}{4} = \frac{6}{100}$
  • Probability (A hits, B misses, C hits) = $\frac{3}{5} \times \frac{3}{5} \times \frac{3}{4} = \frac{27}{100}$
  • Probability (A misses, B hits, C hits) = $\frac{2}{5} \times \frac{2}{5} \times \frac{3}{4} = \frac{12}{100}$

The total probability of exactly two shots hitting is the sum of these probabilities:

P(Exactly 2 hits) = $\frac{6}{100} + \frac{27}{100} + \frac{12}{100} = \frac{45}{100}$

Scenario 2: Exactly Three Shots Hit

This occurs only when all three individuals, A, B, and C, hit the target simultaneously:

$P(A \cap B \cap C) = P(A) \times P(B) \times P(C)$

$P(A \cap B \cap C) = \frac{3}{5} \times \frac{2}{5} \times \frac{3}{4} = \frac{18}{100}$

So, the probability of exactly three shots hitting is P(Exactly 3 hits) = $\frac{18}{100}$

Total Probability Calculation

To find the overall probability that at least two shots hit the target, we add the probabilities calculated for the two scenarios (exactly 2 hits and exactly 3 hits):

P(At least 2 hits) = P(Exactly 2 hits) + P(Exactly 3 hits)

P(At least 2 hits) = $\frac{45}{100} + \frac{18}{100}$

P(At least 2 hits) = $\frac{63}{100}$

Final Answer

The calculated probability that at least two shots hit the target is $\frac{63}{100}$.

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Important Questions from Probability (Notes)

  1. In a box there are 4 white balls and 6 black balls. A ball is drawn at random. If it is white, it is put back along with two more white balls in the box. If it is black, it is put back in the box and then two black balls are thrown out of the box. Now a ball is drawn again at random from the box. Then, what is the probability that it is black?
  2. A fair coin is tossed three times. Let A be the event of getting exactly two heads and B be the event of getting at most
    two tails, then P(A$\cup$B) is:
  3. Bag A contains 3 Red and 4 Black balls while Bag B contains 5 Red and 6 Black balls. One ball is drawn at random from one of the bags and is found to be red. Then, the probability that it was drawn from Bag B is

  4. If we twice flip a balanced coin, what is the probability of getting at least one head?

    1. 1/4
    2. 2/4
    3. 1/6
    4. 3/4
  5. Suppose that the random variable X takes on the values: -1, 0, and 2 with probability $\frac{1}{8}$, $\frac{1}{2}$ and $\frac{3}{8}$. Find the expected value of X.

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