NCERT Exemplar Solutions
Class 10 - Mathematics - CHAPTER 13: Statistics and Probability - Exercise 13.3
Question 23

Question. 23

Die I has faces 1–6. Die II has faces 1,1,2,2,3,3. They are thrown; find probabilities of sums 2 to 9 (separately).

Answer:

Sum23456789
Probability\(\dfrac{1}{18}\)\(\dfrac{1}{9}\)\(\dfrac{1}{6}\)\(\dfrac{1}{6}\)\(\dfrac{1}{6}\)\(\dfrac{1}{6}\)\(\dfrac{1}{9}\)\(\dfrac{1}{18}\)

Detailed Answer with Explanation:

Step 1: Write down the information clearly.

  • Die I is a normal die with 6 faces: 1, 2, 3, 4, 5, 6.
  • Die II is not normal. It has 6 faces too, but the numbers are: 1, 1, 2, 2, 3, 3.

Step 2: Find the total number of outcomes.

  • When two dice are thrown, the number of total outcomes = (number of faces on Die I) × (number of faces on Die II).
  • That is, \(6 \times 6 = 36\).
  • So, there are 36 equally likely outcomes.

Step 3: Understand the sums we need.

  • We want the probabilities of sums = 2, 3, 4, 5, 6, 7, 8, 9.
  • For each sum, we count how many outcomes give that sum.

Step 4: Count outcomes for each sum.

  • Sum = 2: Only possible if Die I = 1 and Die II = 1. But Die II has two faces with "1". So number of outcomes = 2.
  • Sum = 3: (Die I=1, Die II=2) or (Die I=2, Die II=1). Each case repeats twice because Die II has two "1"s and two "2"s. So total outcomes = 4.
  • Sum = 4: Possible by (1,3), (2,2), (3,1). - (1,3): 2 outcomes (because 3 has 2 faces). - (2,2): 2 outcomes (because 2 has 2 faces). - (3,1): 2 outcomes (because 1 has 2 faces). Total = 6.
  • Sum = 5: (2,3), (3,2), (4,1). Each gives 2 outcomes. Total = 6.
  • Sum = 6: (3,3), (4,2), (5,1). Each gives 2 outcomes. Total = 6.
  • Sum = 7: (4,3), (5,2), (6,1). Each gives 2 outcomes. Total = 6.
  • Sum = 8: (5,3), (6,2). Each gives 2 outcomes. Total = 4.
  • Sum = 9: (6,3). Gives 2 outcomes. Total = 2.

Step 5: Convert counts into probabilities.

  • Formula: \( P(E) = \dfrac{\text{Favourable outcomes}}{36} \).
  • Sum = 2: \(\tfrac{2}{36} = \tfrac{1}{18}\).
  • Sum = 3: \(\tfrac{4}{36} = \tfrac{1}{9}\).
  • Sum = 4: \(\tfrac{6}{36} = \tfrac{1}{6}\).
  • Sum = 5: \(\tfrac{6}{36} = \tfrac{1}{6}\).
  • Sum = 6: \(\tfrac{6}{36} = \tfrac{1}{6}\).
  • Sum = 7: \(\tfrac{6}{36} = \tfrac{1}{6}\).
  • Sum = 8: \(\tfrac{4}{36} = \tfrac{1}{9}\).
  • Sum = 9: \(\tfrac{2}{36} = \tfrac{1}{18}\).

Final Note: Always check that the sum of probabilities is 1. \(\tfrac{2+4+6+6+6+6+4+2}{36} = \tfrac{36}{36} = 1\). ✔ Correct!

NCERT Exemplar Solutions Class 10 – Mathematics – CHAPTER 13: Statistics and Probability – Exercise 13.3 | Detailed Answers