Class CBSE Class 12 Mathematics Probability Q #1325
COMPETENCY BASED
UNDERSTAND
3 Marks 2024 AISSCE(Board Exam) SA
A biased die is twice as likely to show an even number as an odd number. If such a die is thrown twice, find the probability distribution of the number of sixes. Also, find the mean of the distribution.

AI Tutor Explanation

Powered by Gemini

Detailed Solution

Step 1: Determine the probabilities of even and odd numbers.

Let $P(\text{odd}) = p$. Then $P(\text{even}) = 2p$. Since the sum of probabilities must be 1, we have: $P(\text{odd}) + P(\text{even}) = 1$ $p + 2p = 1$ $3p = 1$ $p = \frac{1}{3}$ So, $P(\text{odd}) = \frac{1}{3}$ and $P(\text{even}) = \frac{2}{3}$.

Step 2: Calculate the probability of rolling a six.

Since 6 is an even number, the probability of rolling a 6 is $\frac{2}{3}$ divided by the number of even numbers (2, 4, 6), which is 3. Thus, $P(6) = \frac{P(\text{even})}{3} = \frac{2/3}{3} = \frac{2}{9}$ The probability of not rolling a 6 is $P(\text{not 6}) = 1 - P(6) = 1 - \frac{2}{9} = \frac{7}{9}$.

Step 3: Define the random variable and its possible values.

Let $X$ be the number of sixes in two throws. $X$ can take values 0, 1, or 2.

Step 4: Calculate the probabilities for each value of X.

We use the binomial probability formula: $P(X=k) = \binom{n}{k} p^k (1-p)^{n-k}$, where $n=2$ and $p = \frac{2}{9}$. $P(X=0) = \binom{2}{0} (\frac{2}{9})^0 (\frac{7}{9})^2 = 1 \cdot 1 \cdot \frac{49}{81} = \frac{49}{81}$ $P(X=1) = \binom{2}{1} (\frac{2}{9})^1 (\frac{7}{9})^1 = 2 \cdot \frac{2}{9} \cdot \frac{7}{9} = \frac{28}{81}$ $P(X=2) = \binom{2}{2} (\frac{2}{9})^2 (\frac{7}{9})^0 = 1 \cdot \frac{4}{81} \cdot 1 = \frac{4}{81}$

Step 5: Form the probability distribution.

The probability distribution is: $X = 0: P(X=0) = \frac{49}{81}$ $X = 1: P(X=1) = \frac{28}{81}$ $X = 2: P(X=2) = \frac{4}{81}$

Step 6: Calculate the mean of the distribution.

The mean $\mu$ is given by $\mu = \sum x_i P(X=x_i)$. $\mu = 0 \cdot \frac{49}{81} + 1 \cdot \frac{28}{81} + 2 \cdot \frac{4}{81} = 0 + \frac{28}{81} + \frac{8}{81} = \frac{36}{81} = \frac{4}{9}$

Final Answer: Probability Distribution: P(X=0) = 49/81, P(X=1) = 28/81, P(X=2) = 4/81. Mean = 4/9

AI generated content. Review strictly for academic accuracy.

Pedagogical Audit
Bloom's Analysis: This is an UNDERSTAND question because the student needs to understand the concept of probability, probability distribution, and how to calculate the mean of a probability distribution. They also need to understand how the bias in the die affects the probabilities.
Knowledge Dimension: CONCEPTUAL
Justification: The question requires understanding of probability distributions, expected value, and how to apply these concepts to a biased die. It's not just about recalling facts but understanding the underlying principles.
Syllabus Audit: In the context of CBSE Class 12, this is classified as COMPETENCY. The question requires the student to apply their knowledge of probability to a real-world scenario (a biased die) and calculate the probability distribution and mean. This goes beyond simply recalling formulas and requires problem-solving skills.

More from this Chapter

SA
A person is Head of two independent selection committees I and II. If the probability of making a wrong selection in committee I is 0.03 and that in committee II is 0.01, then find the probability that the person makes the correct decision of selection: (i) in both committees (ii) in only one committee.
MCQ_SINGLE
18. The probability that A speaks the truth is $\frac{4}{5}$ and that of B speaking the truth is $\frac{3}{4}$. The probability that they contradict each other in stating the same fact is :
MCQ_SINGLE
If $P(A\cap B)=\frac{1}{8}$ and $P(\bar{A})=\frac{3}{4}$ then $P(\frac{B}{A})$ is equal to :
SA
For the vacancy advertised in the newspaper, 3000 candidates submitted their applications. From the data it was revealed that two third of the total applicants were females and other were males. The selection for the job was done through a written test. The performance of the applicants indicates that the probability of a male getting a distinction in written test is 0.4 and that a female getting a distinction is 0.35. Find the probability that the candidate chosen at random will have a distinction in the written test.
SA
The probability that a student buys a colouring book is 0.7 and that she buys a box of colours is 0.2. The probability that she buys a colouring book, given that she buys a box of colours, is 0.3. Find the probability that the student: (i) Buys both the colouring book and the box of colours. (ii) Buys a box of colours given that she buys the colouring book.
View All Questions