Atest has 20 questions. how many do you need to answer correctly in order to get 4/5 of them right?

The answer is:  " 16 " .

Explanation:

Method 1)

(4/5) *(20/1) = ?  

The "5" cancels to a "1" ; and the "20" cancels to a "4" ;  
   (since "20÷5=4" ; and "5÷5=1") ;

Rewrite as:  (4/1) * (4/1) = 4 * 4 = 16.

Method 2)

4/5 * 20/1  = (4*20)/(5*1) = (80/5) = 16 .

Method 3)

4/5 * 20 = ?  ;

4/5 = 8/10 = 0.8 ;

0.8 * 20 = 16.0 = 16.