The average of 30 numbers is 40 and that of other 40 numbers is 30. The average of all the numbers is :

Answer: Option A

According to the question,
Average of 30 numbers is = 40
Sum of 30 numbers is = 40 × 30 = 1200
Average of 40 numbers is = 30
Sum of 40 numbers is = 40 × 30 = 1200
Total average = $$\frac{1200+1200}{70}$$
= $$\frac{2400}{70}$$
= $$34\frac{2}{7}$$