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Question

A canal system is shown in the figure. 

Water flows from A to B through two channels. Gates $G_1$ and $G_2$ are operated independently to regulate the flow. Probability of $G_1$ to be open is 10% while that of $G_2$ is 20%. The probability that water will flow from A to B is

The correct answer is
28%

To calculate the probability of water flowing from A to B, we need to consider the scenarios in which the gates $G_1$ and $G_2$ are open because water can only flow if at least one gate is open.

Given:

  • Probability of $G_1$ being open, \(P(G_1) = 0.10\)
  • Probability of $G_2$ being open, \(P(G_2) = 0.20\)

The probability that both gates are closed is calculated as follows:

  • Probability that $G_1$ is closed = \(1 - P(G_1) = 0.90\)
  • Probability that $G_2$ is closed = \(1 - P(G_2) = 0.80\)

Therefore, the probability that both gates are closed is the product of both individual probabilities:

\(P(\text{Both Closed}) = 0.90 \times 0.80 = 0.72\)

Thus, the probability that at least one gate is open, allowing water to flow, is:

\(P(\text{At least one open}) = 1 - P(\text{Both Closed}) = 1 - 0.72 = 0.28\)

So, the probability that water will flow from A to B is 28%.

Therefore, the correct answer is 28%.

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Important Questions from Probability (Notes)

  1. In a class, 40% and 20% students passed in Mathematics and Physics, respectively, and 10% students passed in both subjects. What is the probability of a randomly selected student to have passed in Physics if the student already passed in Mathematics?
  2. A stick of length L is broken into two pieces at random. What is the average length of the smaller piece?
  3. Two students are solving the same problem independently. If the probability that the first one solves the problem is $\frac{3}{5}$ and the probability that the second solves the problem is $\frac{4}{5}$, what is the probability that at least one of them solves the problem?
  4. A fair die was thrown three times and the outcome was repeatedly six. If the die is thrown again what is the probability of getting six?
  5. 12 balls, 3 each of the colours red, green, blue and yellow are put in a box and mixed. If 3 balls are picked at random, without replacement, the probability that all 3 balls are of the same colour is
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