Answer:
 A good rule is to change 10 to 15 percent of the water each week. If your tank is heavily stocked, bump that up to 20 percent each week. A lightly stocked aquarium can maybe get by for two to four weeks, but this should be the maximum length of time between water changes.
Step-by-step explanation:
This is the correct answer you want
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Answer:
1:3
Step-by-step explanation:
Since your scaling down you divide the smaller number by the larger number
7/21=1/3
=1:3
Hope this helps :)
 
        
             
        
        
        
Answer:
D.  none
Step-by-step explanation:
The point in geometry is defined as the location.
Point A is described as the location of A on any given plane.
Point is represented as a dot.
A dot has no physical dimension like depth,  height, thickness or size.
Hence, any two points can not be compared on the basis of any physical parameter.
 
        
                    
             
        
        
        
I would say true. Hope this helps :)
        
                    
             
        
        
        
Answer:
I think that it might be two.
Step-by-step explanation: