How do I solve this problem?

Question

Less than half of the students missed the chemistry demonstration. in fact only 3/10 of the students missed the demonstration. If 21 students did not miss the demonstration, how many students did miss the demonstration?

Answer 1

If 3/10 students missed the demonstration, that means that 7/10 students attended the demonstration.

 

Because we know that 21 students attended the demonstration and this is 7/10 of all the students, we can calculate the total number of students x using the following equation:

 

(7/10) (x) = 21

 

x = 21/0.7 = 30

 

Because the total number of students is 30, and 21 students attended the demonstration, then 9 students missed the demonstration.

 

Answer: 9 students missed the demonstration