In order to accurately rank these numbers from smallest to greatest, we will need to convert them all to decimals.
0.8 is already in decimal form, so we will leave it alone for now.
Percentages can be converted into decimals by either dividing them by 100, or (my personal shortcut) just moving the decimal point two places to the left. Using either of these methods, 30% in decimal form becomes 0.3.
3/5 is a little harder to work with, but I already know that 1/5 is 0.2, and since there's 3 of those 1/5s, we just need to multiply 0.2 by 3, which is 0.6.
0.8 is still 0.8
30% has become 0.3
3/5 is now 0.6
Now, we can see that some of these are clearly greater than others.
If we put them in order from smallest to greatest, it becomes
0.3 < 0.6 < 0.8.
Transforming them back into their original forms, we can say that in order from smallest to greatest the three numbers are listed in this way: 30%, 3/5, 0.8.
Hope that helped =)