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