21 students sleep for 9 hours each night
<em><u>Solution:</u></em>
Given that, Mr.Lee wants to survey 20 of the 210 students in seventh grade about the hours they sleep each night
He finds 2 of the 20 students surveyed sleep for 9 hours each night
Therefore, 2 out of 20 students sleep for 9 hours each night
Find out the percentage of 2 out of 20
Thus 10 % of 210 students sleep for 9 hours each night
Find out 10 % of 210
Thus 21 students sleep for 9 hours each night