All the numbers begin with 2 so we only have to get the fractions or decimals in order.
1/2, 0.4, 0.35, 1/8. Put the fractions in order: 1/2 is bigger than 1/8; decimals in order: 0.4 is bigger than 0.35.
1/2 in decimal is 0.5 and 1/8 is 0.125. So we can see the order is 1/2, 0.4, 0.35, 1/8.
Now we add back the 2: 2 1/2, 2.4, 2.35, 2 1/8.