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Question

Take two long dice (rectangular parallelepiped), each having four rectangular faces labelled as 2, 3, 5, and 7. If thrown, the long dice cannot land on the square faces and has 1/4 probability of landing on any of the four rectangular faces. The label on the top face of the dice is the score of the throw.
If thrown together, what is the probability of getting the sum of the two long dice scores greater than 11?

The correct answer is
3/16

Understanding the Dice Probabilities

We are given two identical long dice. Each die has four rectangular faces labeled with scores: 2, 3, 5, and 7.

The dice cannot land on the square faces. This means each of the four labeled faces has an equal probability of being the top face when a die is thrown.

The probability of landing on any specific face (2, 3, 5, or 7) for a single die is $P(\text{face}) = \frac{1}{4}$.

Calculating Total Possible Outcomes

When two such dice are thrown together, the total number of possible outcomes is the product of the number of outcomes for each die.

Total Outcomes = (Number of faces on Die 1) $\times$ (Number of faces on Die 2)

Total Outcomes = $4 \times 4 = 16$.

Each of these 16 outcomes is equally likely because the individual face probabilities are equal.

Identifying Favorable Outcomes (Sum > 11)

We need to find the pairs of scores (Die 1, Die 2) whose sum is greater than 11.

Let's list the possible pairs systematically:

  • If Die 1 = 2, the required score on Die 2 must be > 9 (impossible with faces {2, 3, 5, 7}).
  • If Die 1 = 3, the required score on Die 2 must be > 8 (impossible).
  • If Die 1 = 5, the required score on Die 2 must be > 6. The only possibility is Die 2 = 7. Pair: (5, 7).
  • If Die 1 = 7, the required score on Die 2 must be > 4. Possible scores are Die 2 = 5 or Die 2 = 7. Pairs: (7, 5), (7, 7).

The pairs of scores resulting in a sum greater than 11 are (5, 7), (7, 5), and (7, 7).

Number of Favorable Outcomes = 3.

Determining the Probability

The probability of an event is calculated as the ratio of the number of favorable outcomes to the total number of possible outcomes.

Probability (Sum > 11) = $\frac{\text{Number of Favorable Outcomes}}{\text{Total Possible Outcomes}}$

Probability (Sum > 11) = $\frac{3}{16}$.

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Important Questions from Probability

  1. Two dice are thrown simultaneously. What is the probability of getting the same number on both the dice?

  2. The probability of being 53 Sundays in year 2020 is-

  3. Three dice are thrown randomly. The probability of coming 3 in at least one die is

  4. The probability of having 53 Tuesdays in an ordinary year is:

  5. When two dice are tossed simultaneously, the probability that the sum of the numbers appearing on both the dice is 8 will be

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