CA Foundation · Quantitative Aptitude · Probability
If E(X) = 8 and E(X²) = 70, what is the expected value E(3X - 2) and the variance of X respectively?
E(3X-2) equals 3 times 8 minus 2, which is 22. The variance is E(X²) minus the square of E(X), that is 70 minus 64, giving 6.
- A22 and 6Correct
- B22 and 62
- C24 and 6
- D26 and 6
Explanation
E(3X-2) = 3(8) - 2 = 22. Variance = E(X²) - [E(X)]² = 70 - 64 = 6. Using 70 - 8 = 62 is a mistake, as the mean must be squared. Option with 24 forgets the subtraction of 2.
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