3x15=45 and 17x15=255 so 45+255=300
        
                    
             
        
        
        
24 Blue marbles. 
Explanation: 
56 - 8 = 48
48 / 2 = 24
so if there are 24 blue marbles, 24 x 2 = 48, and then 8 more is 56.
 
        
                    
             
        
        
        
Answer:
50 gallons of each.
Step-by-step explanation:
 
        
             
        
        
        
Answer:
   18
Step-by-step explanation:
A two-digit number (xy) will have the value 10x+y. The sum of its digits is x+y.
You want ...
   10x +y = 2(x +y)
   1 ≤ x ≤ 9
   0 ≤ y ≤ 9
The equation can be simplified to ...
   8x = y
The only single-digit values for x and y that satisfy the requirements are ...
   x = 1, y = 8
The two-digit number of interest is 18.
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<em>Check</em>
Its sum of digits is 1+8 = 9. 2×9 = 18.
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<em>Comment on the relationship in the problem</em>
Many of us learned our multiplication tables for 9s by remembering that the sum of digits of 9n was 9, and that the leading digit of the product was n-1.