Probability of winning mega million?

138 Views Asked by At

Initially I thought it would be

$\left(\frac{1}{70}\right)^5\left(\frac{1}{25}\right)$

to get the probability of choosing the right number out of 70 exactly 5 times and then the 6th number out of 25.

Then I saw that it was actually

${70\choose{5}}*25$

What exactly is the difference and why is the first one not correct?

1

There are 1 best solutions below

4
On

For your attempts, you wouldn't want to repeat the same number. Once a number is chosen, you wouldn't want to choose it again. Also order shouldn't matter.

Also, for the answer that you show us, that can't be a probability, as it is the number of possibility. Just invert it to get the probability.