This is because Andrea converted the Percentage wrong.
to Convert a Percent to a Decimal, she should have divided by 100
so  5 divided by 100 = 0.05  [not 0.5]
Andrea should have multiplied 300 by 0.05 instead to get the right answer
quickly finding 10% of a number means to simply move the decimal to the left one place
so  10% of 300 is 30
since  5% is half of 10%
half of 30 is 15
and so  5% of 300 is 15
        
             
        
        
        
A. 
Mice are small and kilograms are for much larger objects. The other two measurements are for liquids. 
        
                    
             
        
        
        
A trapezoid is isosceles if and only if 
(1)	The base angles are congruent
(2)	The diagonals are congruent
(3)	The opposite angles are supplementary
So the description does not guarantee that a trapezoid is isoceles for "Congruent bases".