6/7 = 7 choose 6.
1/3=4/ 12
1/4=3/ 12
1/6=2/ 12
Let's add them up.
4/ 12+3/ 12+2/ 12=9/ 12
1 minus 9/ 12.
1-9/ 12=3/ 12
In other words, 3/ 12 of the total is 3.