MHB Probability question where an object is chosen randomly out of two objects

  • Thread starter Thread starter tantrik
  • Start date Start date
  • Tags Tags
    Probability
AI Thread Summary
The probability problem involves two opera singers, Mario and Clarissa, with different review probabilities from two newspapers. The initial calculation incorrectly considered only one newspaper, leading to an incorrect probability of 1/6 for both recitals being reviewed. The correct approach requires calculating the probabilities for both newspapers, resulting in a combined probability of 13/60 for both recitals being reviewed. The discussion clarifies the importance of accounting for all possible outcomes when calculating probabilities. Understanding these principles is essential for solving similar probability problems accurately.
tantrik
Messages
13
Reaction score
0
Dear friends,

I am stuck at the following probability problem. Will appreciate your help.

Two opera singers, Mario and Clarissa both perform on the same night, in separate recitals. The independent probabilities that two newspapers X and Y publish reviews of their recitals are given below:

Probability of review in newspaper X
================================ ====
Mario's recital - 1/2
Clarissa's recital - 2/3

Probability of review in newspaper Y
================================ ====
Mario's recital - 1/4
Clarissa's recital - 2/5

Mario buys one of the newspapers at random. What is the probability that it has reviewed "both" recitals?


I did this way: P(reviewed both recitals) = P(buys paper X)*P(X reviews Mario)*P(X reviews Clarissa) = (1/2)*(1/2)*(2/3) = 1/6

But 1/6 is not the correct answer. Let me know where I am wrong and why.

Thanks in advance.
 
Mathematics news on Phys.org
Your answer is wrong because it refers only to newspaper X! You calculated "the probability that she bought newspaper X and both were reviewed". If she had bought newspaper Y then the probability both are reviewed is (1/4)(2/5)= 1/10. The probability she bought newspaper Y was 1/2 so the probability she bought newspaper Y and both were reviewed is (1/2)(1/10)= 1/20. The probability both were reviewed in whatever paper she bought is the sum: 1/20+ 1/6= 3/60+ 10/60= 13/60.
 
HallsofIvy said:
Your answer is wrong because it refers only to newspaper X! You calculated "the probability that she bought newspaper X and both were reviewed". If she had bought newspaper Y then the probability both are reviewed is (1/4)(2/5)= 1/10. The probability she bought newspaper Y was 1/2 so the probability she bought newspaper Y and both were reviewed is (1/2)(1/10)= 1/20. The probability both were reviewed in whatever paper she bought is the sum: 1/20+ 1/6= 3/60+ 10/60= 13/60.

Thanks for the solution. Now I understand where the mistake was.
 
Suppose ,instead of the usual x,y coordinate system with an I basis vector along the x -axis and a corresponding j basis vector along the y-axis we instead have a different pair of basis vectors ,call them e and f along their respective axes. I have seen that this is an important subject in maths My question is what physical applications does such a model apply to? I am asking here because I have devoted quite a lot of time in the past to understanding convectors and the dual...
Insights auto threads is broken atm, so I'm manually creating these for new Insight articles. In Dirac’s Principles of Quantum Mechanics published in 1930 he introduced a “convenient notation” he referred to as a “delta function” which he treated as a continuum analog to the discrete Kronecker delta. The Kronecker delta is simply the indexed components of the identity operator in matrix algebra Source: https://www.physicsforums.com/insights/what-exactly-is-diracs-delta-function/ by...
Back
Top