What mistake did Kendra make?

Question

In Kendra’s class, 40 percent of the students earned an A on the math test. Twenty students earned an A. Kendra needs to find out how many students are in her class. Kendra’s work is shown below.



What mistake did Kendra make?  

Answer 1

She should have divided the denominator by 2:

part/whole=40/100=(40➗2)/(100➗2)=20/50, so there were 50 students in the class.