The average height of 30 girls out of a class of 40 is 160 cm. and that of the remaining girls is 156 cm. The average height of the whole class is : Choose the correct choice from the following answers:
A) 158 cms	B) 158.5 cms	C) 159 cms	D) 159.5 cms	E) none

Rationale: explanation : average height of the whole class = ( 36 × 160 + 10 × 156 / 40 ) = 159 cms answer c
Answer: C