What is the order from greatest to least 5/8 , 0.5, 2/5, 0.78

To solve you would first convert all of the numbers into the same form by dividing the numerators by the denominators of the fractions to create the decimal. This would leave you with 5/8=0.625, 0.5, 2/5=0.4, 0.78. From here you can determine the greatest to least by looking at the right of the decimal and ordering them chronologically. 
The final answer would be 0.78, 5/8, 0.5, 2/5
Hope I helped :)