Broderick answered 21 of the 25 questions on his history test correctly. what decimal represents the fraction of problems he answered incorrectly?

THE ANSWER IS 0.84 I just multiplied 25 and 21 by four to get 84 over 100 to easily convert to a decimal. 
84 hundredths  

Best answer that i found on yahoo ok   set :   x= length of 2nd piece in cm  x- 3= length of 1st piece in cm  x-4= length of 3rd piece in cm  then since you know they all came from the 20 cm ribbon you add them together and set them equal to 20x+ x-3 +x-4 = 20  3x - 7= 20  3x= 27  x= 9  the shortest piece is the third piece which is x- 4  x-4  9-4 = 5  the length of the smallest piece is 5 cm.  the other lengths are  9 cm  6 cm