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.