Question 284719
20 girls avg age =15

15 boys avg age =16 

Total 40 avg age = 17

Let the average age of adults be x.  5 adults

Total age of all students / total students = 17

5x+15*16+20*15 / 40 = 17

5x+240+300=40*17

5x+540=680

5x=680-540

5x=140

x= 140/5

x= 28

The average age of adults = 28