The numbers 1 through 10 are written in separate slips of paper, and the slips are placed into a box. Then, 4 of these slips are drawn at random.
What is the probability that the drawn slips are "1", "2", "3", and "4", in that order

Respuesta :

Since you want those numbers to appear in that precise order, you only change is to extract 1 with the first draw, 2 with the second, and so on.

You have 10 slips at the beginning, so the probability of having 1 at the first draw is

[tex] \dfrac{1}{10} [/tex]

Now you have 9 slips left, so the probability of picking 2 with the second draw is

[tex] \dfrac{1}{9} [/tex]

Similarly, the remaining probabilities are [tex] \frac{1}{8} [/tex] and [tex] \frac{1}{7} [/tex]

You want these events to happen one after the other, and they are independent. So, the overall probability is the product of the single probabilities:

[tex] P = \dfrac{1}{10}\cdot\dfrac{1}{9}\cdot\dfrac{1}{8}\cdot\dfrac{1}{7} = \dfrac{1}{10\cdot9\cdot8\cdot7} = \dfrac{1}{5040} [/tex]