In a class of 60 students, the average height of 20 students is x centimeter, the average height of other 20 students is y centimeter and the average height of the remaining 20 students is z centimeter. Find the average height of the whole class.
1
(x + y + z)/60 cm
2
30 cm
3
(x + y + z)/20 cm
4
(x + y + z)/3 cm