First change them all into either fractions or decimals. Decimals are probably easier though. 1/5 = 0.2; 12/25 = 0.48; 4/5 = 0.8
Order: 0.2, 0.35, 0.48, 0.5, 0.8
Then you change the decimals that you converted back into the fraction form
Answer: 1/5, 0.35, 12/25, 0.5, 4/5
