Table of Contents
Exercise 13.1 Solutions
Probability – Class X Mathematics
State Council of Educational Research and Training, Telangana, Hyderabad
Question 1: Complete the following statements
Solution: The sum of the probability of an event and its complement is always 1.
\[ P(E) + P(\text{not } E) = 1 \]
Solution: The probability of an impossible event is 0. Such an event is called an impossible event.
\[ P(\text{Impossible event}) = 0 \]
Solution: The probability of a certain event is 1. Such an event is called a sure event.
\[ P(\text{Certain event}) = 1 \]
Solution: The sum of probabilities of all elementary events of an experiment is 1.
\[ \sum P(E_i) = 1 \]
Solution: The probability of any event \( E \) satisfies:
\[ 0 \leq P(E) \leq 1 \]
Question 2: Which of the following experiments have equally likely outcomes? Explain.
Solution: Not equally likely. The probability depends on the car’s condition, fuel, etc.
Solution: Not equally likely. The outcome depends on the player’s skill.
Solution: Equally likely. There’s a 50% chance of guessing correctly.
\[ P(\text{Right}) = P(\text{Wrong}) = 0.5 \]
Solution: Equally likely (assuming equal probability for biological sexes).
\[ P(\text{Boy}) = P(\text{Girl}) ≈ 0.5 \]
Question 3: If \( P(E) = 0.05 \), what is the probability of ‘not E’?
Solution:
We know that \( P(E) + P(\text{not } E) = 1 \)
\[ P(\text{not } E) = 1 – P(E) = 1 – 0.05 = 0.95 \]
Question 4: A bag contains lemon flavoured candies only. Malini takes out one candy without looking into the bag.
Solution: Since the bag contains only lemon flavored candies:
\[ P(\text{Orange}) = 0 \] (Impossible event)
Solution: Since all candies are lemon flavored:
\[ P(\text{Lemon}) = 1 \] (Certain event)
Diagram: A bag containing multiple lemon candies (all yellow) with one being drawn out.
[Illustration of a bag with yellow candies and one hand taking a candy out]
Question 5: Rahim removes all the hearts from the cards. What is the probability of:
Solution: Original deck has 52 cards. After removing 13 hearts, 39 cards remain.
Number of aces in remaining cards: 3 (since Ace of Hearts was removed)
\[ P(\text{Ace}) = \frac{3}{39} = \frac{1}{13} \]
Solution: All 13 diamonds remain in the deck of 39 cards.
\[ P(\text{Diamond}) = \frac{13}{39} = \frac{1}{3} \]
Solution: Since all hearts have been removed, all remaining 39 cards are not hearts.
\[ P(\text{Not heart}) = \frac{39}{39} = 1 \]
Solution: Since all hearts have been removed:
\[ P(\text{Ace of Hearts}) = 0 \] (Impossible event)
Diagram: A standard deck of cards with all heart cards (red) removed, showing only clubs, diamonds, and spades remaining.
[Illustration of a partial deck with hearts missing]
Question 6: In a group of 3 students, the probability of 2 students not having the same birthday is 0.992. What is the probability that the 2 students have the same birthday?
Solution:
Let \( P(\text{Same}) \) be the probability that two students share a birthday.
Given \( P(\text{Not same}) = 0.992 \)
\[ P(\text{Same}) = 1 – P(\text{Not same}) = 1 – 0.992 = 0.008 \]
Question 7: A die is rolled once. Find the probability of getting:
Solution: Prime numbers on a die: 2, 3, 5 (3 outcomes)
Total possible outcomes: 6
\[ P(\text{Prime}) = \frac{3}{6} = \frac{1}{2} \]
Solution: Numbers between 2 and 6: 3, 4, 5 (3 outcomes)
\[ P(\text{Between 2 and 6}) = \frac{3}{6} = \frac{1}{2} \]
Solution: Odd numbers on a die: 1, 3, 5 (3 outcomes)
\[ P(\text{Odd}) = \frac{3}{6} = \frac{1}{2} \]
Diagram: A standard six-faced die showing numbers 1 through 6 with prime numbers (2,3,5) highlighted.
[Illustration of a die with some numbers highlighted]
Question 8: What is the probability of selecting a red king from a deck of cards?
Solution:
Total cards in deck: 52
Red kings: King of Hearts and King of Diamonds (2 cards)
\[ P(\text{Red King}) = \frac{2}{52} = \frac{1}{26} \]
Diagram: A deck of cards showing the two red kings (King of Hearts and King of Diamonds).
[Illustration of two red king cards]
Question 9: Make 5 more problems of this kind using dice, cards or birthdays
Sample Problems:
- What is the probability of rolling a number greater than 4 on a standard die?
- If two cards are drawn from a standard deck without replacement, what is the probability both are spades?
- In a group of 30 people, what is the probability that at least two people share the same birthday?
- What is the probability of drawing a face card (Jack, Queen, King) from a standard deck?
- If you roll two dice, what is the probability that the sum is 7?
These problems can be discussed with friends and teachers to understand probability concepts better.