When rolling two six faced dice, what is the probability the sum equal to seven?

What you want is P (6∩1) or P (1∩6) or P (2∩5) or P (5∩2) or P (3∩4) or P (4∩3).

The events of rolling the dice are independent (i. e. they don't affect one another) so:

E. g.

P (6∩1) = P (6) * P (1)

P (2∩5) = P (2) * P (5)

The probability of getting a given number on a roll is 1/6 for both dice.

So:

P (6∩1) = 1/6 * 1/6 = 1/36

This is the same for any arrangement of numbers you could get from rolling two dice.

So, we can see that there are 6 arrangements of numbers that will give a sum of 7 and so that is 6 * 1/36 = 6/36 = 1/6