We have 9 boy kittens and 6 girl kittens, a total of 15 kittens.
9 cats will be selected and we have to calculate the probability that 5 boy kitttens and 4 girl kittens are chosen.
We could have modeled as a binomial experiment, but the probability of choosing a boy kitten is not constant after each selection. Then, we have to select an alternative method.
We can think of it of a combinatorial problem.
In this case, it is a combination problem, as the order of selection does not matter and each kitten is equivalent within its category.
Repetition is not allowed: a kitten selected can not be selected again.
We can start finding all the possible combinations for 9 kittens out of the total 15 kittens:
The probability of selecting 5 boys and 4 girls will be the relation between the outcomes where there are 5 boys and 4 girls and the total number of outcomes we have just calculated.
Then, we can now calculate how many combinations of 9 kittens have 5 boys and 4 girls as a product of two combinations: the combinations for the boys C(9;5) and the combinations for the girls C(6;4).
We can calculate this as:
We can now calculate the probability as the ratio of combinations 1890/5005:
Answer: the probability is 0.378.