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Question

Two dice are thrown simultaneously. The probability that the product of the numbers appearing on the top faces of the dice is a perfect square is

The correct answer is
2/9

Dice Probability: Product as Perfect Square

When two dice are thrown simultaneously, each die has 6 possible outcomes (numbers 1 through 6). The total number of possible outcomes is the product of the outcomes for each die.

Total possible outcomes = $6 \times 6 = 36$.

Identifying Favorable Outcomes

We need to find the outcomes where the product of the numbers on the two dice ($d_1 \times d_2$) is a perfect square. A perfect square is a number that is the square of an integer (e.g., 1, 4, 9, 16, 25, 36, ...).

Let's list the pairs $(d_1, d_2)$ such that $d_1 \times d_2$ is a perfect square, where $d_1, d_2 \in \{1, 2, 3, 4, 5, 6\}$:

  • If the product is 1: (1, 1)
  • If the product is 4: (1, 4), (4, 1), (2, 2)
  • If the product is 9: (3, 3)
  • If the product is 16: (4, 4)
  • If the product is 25: (5, 5)
  • If the product is 36: (6, 6)

The set of favorable outcomes is {(1, 1), (1, 4), (4, 1), (2, 2), (3, 3), (4, 4), (5, 5), (6, 6)}. The total number of favorable outcomes is 8.

Calculating the Probability

Probability is calculated as the ratio of the number of favorable outcomes to the total number of possible outcomes.

$ P(\text{Product is a perfect square}) = \frac{\text{Number of Favorable Outcomes}}{\text{Total Number of Outcomes}} $

$ P(\text{Product is a perfect square}) = \frac{8}{36} $

Simplifying the fraction gives:

$ \frac{8}{36} = \frac{2 \times 4}{9 \times 4} = \frac{2}{9} $

The probability that the product of the numbers appearing on the top faces of the dice is a perfect square is 2/9.

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Important Questions from Probability

  1. Three dice are thrown. What is the probability of getting a sum which is a perfect square?

  2. Two distinct natural numbers from 1 to 9 are picked at random. What is the probability that their product has 1 in its unit place?

  3. Two dice are thrown. What is the probability that difference of numbers on them is 2 or 3 ?

  4. Suppose that there is a chance for a newly constructed building to collapse, whether the design is faulty or not. The chance that the design is faulty is 10%. The chance that the building collapses is 95% if the design is faulty, otherwise it is 45%. If it is seen that the building has collapsed, then what is the probability that it is due to faulty design?

  5. What is the probability that all three boys sit together?

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