Q. The average of 30 numbers is 40 and that of other 40 numbers is 30. The average of all the numbers is :
Answer: $latex 34\frac{2}{7}&s=1$
Notes: Average of all numbers = $latex = \frac{30\times 40 + 40\times 30}{70}&s=1$ $latex = \frac{2400}{70} = 34\frac{2}{7}&s=1$ Hence option [B] is correct answer

3