CA Foundation · Quantitative Aptitude · Probability
A fair die is thrown once. If X is the number shown on the upper face, what is the mathematical expectation E(X)?
The expectation is 3.5. Each face from 1 to 6 has probability 1/6, so E(X) is the sum 21 multiplied by 1/6, which equals 3.5. Expectation need not be a value the die can actually show.
- A3
- B3.5Correct
- C4
- D4.5
Explanation
Each face has probability 1/6. E(X) = (1+2+3+4+5+6)/6 = 21/6 = 3.5. Option 3 wrongly takes the middle integer, ignoring that expectation is the probability-weighted mean.
Did you get it right without looking?
One question tells you little. A timed set on Probability shows your real accuracy, how long you take and where you lose marks.
More Probability questions
- For events A and B, P(A) = 0.6, P(B) = 0.5 and P(A ∪ B) = 0.8. What is P(B | A)?
- Three urns hold balls as follows: Urn I has 2 white and 3 black, Urn II has 4 white and 1 black, Urn III has 3 white and 2 black. An urn is …
- Two fair dice are rolled together. What is the probability that the sum of the numbers shown is greater than 10?
- A box contains 4 defective and 6 good bulbs. Two bulbs are drawn one after another without replacement. Given that the second bulb is good, …
- A number is chosen at random from the integers 1 to 60. What is the probability that it is divisible by 4 or by 6 but not by both?
- A box contains 6 white and 4 black balls. Two balls are drawn one after another without replacement. What is the probability that the first …