The average height of 40 girls out of a class of 50 is 169 cm. and that of the remaining girls is 167 cm. The average height of the whole class is :	Choose the correct choice from the following answers
A) 138.9 cms
B) 149.2 cms
C) 168.6 cms
D) 159.2 cms
E) 142.5 cms

Rationale: "explanation : average height of the whole class = ( 40 × 169 + 10 × 167 / 50 ) = 168.6 cms answer c"
Answer: C