Probability

CFA Level I Quant
#1
  • A very large company has twice as many male employees relative to female employees. If a random sample of four employees is selected, what is the probability that all four employees selected are female? A. 0.3333. B. 0.0625. C. 0.0123. Amswer C: Since there are twice as many male employees to female employees, P(male) = 2/3 and P(female) = 1/3. Therefore, the probability of 4 successes = (0.333)^4 = 0.0123.

This iw what I thought.

If you select one female, now there is one female employee less. I assumed 10 females and 20 males

shouldn’t the probability be like below?

10/20 * 9/19 * 8/18 * 7/17 ???

thanks

#2

Presumably, “large” means “large enough that if you yank out one employee of either sex, the probabilities remain the same (to four decimal places)”.

If the company had 30 employees, then your calculation is correct in principle, but incorrect in execution:

10/ 30 × 9/ 29 × 8/ 28 × 7/ 27

They could have done a better job on the question.

#3

got it… thanks…

its tough trying to remember formula and also focusing on words to find out the meaning and assumption…