Answer:

The probability of choosing tiles which sum is 12 is 1/21

Step-by-step explanation:

The numbers we have is 1.2,3,4,5,6 and 7

The sum we are looking at is 12. The only sum that can give us this sum is the addition of 7 and 5

There are only two ways we can make this selection if order matters.

Either we pick 5 first then 7 second or 7 first and 5 second

The probability of picking a 5 first will be 1/7, since it is without replacement , the probability of picking a 7 next will be 1/6

The joint probability here would thus be 1/7 * 1/6 = 1/42

In the other second case where we are picking a 7 first and a 5 second, the probability here will be the same as first just that we reversed the other. Hence, the probability here is also 1/42

Now, the probability of either of the two orders happening will be 1/42 + 1/42 = 2/42 = 1/21