1/3, 2/6, 3/9, 4/You see the pattern? The denominator is by 3's. You can also see it as 1*3=3, 2*3=6, 3*3=6, then 4*3=12
So, the last fraction would be 4/12.
1/2, 2/4, 3/6, 4/8, 5/ , 6/ The denominator is by 2's.
1*2=2, 2*2=4, 3*2=6, 4*2=8, 5*2=10,6*2=12
So, the last two fractions would be 5/10, and 6/12.