The mean heights of three groups of students consisting of 20, 16 and 14 students each are 1.67 m, 1.50 m and 1.40 m respectively. Find the mean height of all the students.
Worked solution (try it first)
Find each group's total height: 20×1.67=33.4, 16×1.50=24 and 14×1.40=19.6.
All together: 33.4+24+19.6=77 m for 20+16+14=50 students.