John rolls a number cube twice. What is the probability that the sum of the 2 rolls is less than 7, given that the first roll is a 1?

one over six

one over three

one over two

five over six

The probability would be 5/6.

There are 6 ways we can roll two dice and have the first number be a 1:

1, 1

1, 2

1, 3

1, 4

1, 5

1, 6

Out of these, 5 possibilities give us a sum less than 7:

1, 1

1, 2

1, 3

1, 4

1, 5

Thus we have 5/6.