CA Foundation · Quantitative Aptitude · Probability
If X is a random variable with E(X) = 8, what is E(3X - 5)?
E(3X - 5) equals 19. Expectation is linear, so E(aX + b) = aE(X) + b. Substituting a = 3, b = -5 and E(X) = 8 gives 3 times 8 minus 5, which is 24 minus 5, equal to 19.
- A24
- B19Correct
- C29
- D21
Explanation
Using E(aX + b) = aE(X) + b, E(3X - 5) = 3(8) - 5 = 19. The value 24 ignores the constant, and 21 wrongly multiplies the constant by 3 as well (3(8-5) is 9, not 21; 21 comes from 3*8 - 3).
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