Answer:
-8, -1.5 , -1/2 , 1/4 , 2.5, 3 , 11/2 (if is not 11/2 but 1 and 1/2) the answer is : -8, -1.5 , -1/2 , 1/4 , 1/2, 1 , 2.5, 3 
Explanation:
First of all we have to express the decimal numbers with a fraction 
2.5 = 25/10 = 5/2 
-1.5 = -15/10 = -3/2 
now we have to express al numbers with a fraction with the same denominator. In this case the value that help us the most is 4 
-1/2 = -2/4 
5/2 = 10/4 
-8 = -32/4 
1/4 = 1/4 
11/2 = 22/4 
-3/2 = -6/4 
3 = 12/4 
now we have to check only the numerators for discover the order of the numbers. So from the least to the greatest we have: 
-32/4 ; -6/4 ; -2/4 ; 1/4 ; 10/4 ; 12/4 ; 22/4 
the final step is rewrite the original numbers in this order 
-8, -1.5 , -1/2 , 1/4 , 2.5, 3 , 11/2