What volume of water would be added to 16.5 ml of a 0.0813 m solution of sodium borate in order to get a 0.0200 m s?

When diluting solutions from concentrated solutions the following formula can be used 
c1v1 = c2v2 
where c1 is concentration and v1 is volume of the concentrated solution 
and c2 is concentration and v2 is volume of the diluted solution to be prepared
substituting these values 
0.0813 M x 16.5 mL = 0.0200 M x V
V = 67.1 mL
the volume of the diluted solution prepared is 67.1 mL.
the volume of water that should be added to get a final volume of 67.1 mL is (67.1 - 16.5 ) = 50.6 mL
a volume fo 50.6 mL should be added 

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