An unlikely probability

https://app.dataquest.io/m/378/probability-rules/4/the-addition-rule

Hi I got stuck on this question during one of the probability courses.

I assumed the question:
The sum is either even or less than 2 — assign your answer to p_even_or_less_2

would amount to the answer 1/36.

Since there is only one possibility to score a 2 (less is impossible) out of 36. But low and behold the answer states an 18/36th chance.

I’ve read the question over maybe 10x to see if I’m missing something

The addition rule of probability is P(A U B) = P(A) + P(B) - P(A and B). Therefore this question translates to the following probability P(Even or Less 2) = P(Even) + P(Less 2) - P(Even and Less 2).

But P(Even) = 18/36, summing all the even numbers on the table
P(Less 2) = 0 since no numbers less than 2
and P(Even and Less 2) = 0. since no intersection between Even and Less 2.

Therefore P(Even or Less 2) = 18/36

2 Likes

Ah I assumed even meant “==” or equal to in this context… That’s my mother language throwing me off (dutch) Feel a bit silly now, thanks for the elaborate answer anyways. Have a good one!

2 Likes