Answer:
1000 students
Explanation:
First, what fraction is left of 2/5? 3/5!! Now you can set up a proportion. 3/5 is equal to 600/??? Simple. 5 * 600 = 3000. 3000 / 3 = 1000. That's the total number of students, your answer!
For further understanding:
This means that 400 students doubt. 400/1000 and 2/5 both equal 0.4, so that is a clue to know you are right.