$A, B, C$ and $D$ are four consecutive odd numbers and their average is $42 .$ What is the product of $B$ and $D$ ?

A man travels by a car to his office at $60 \,km / h$ and returns home along the same route at $20 \,km / h .$ Find the average speed of his whole journey. (in $km/h$)

Out of seven given numbers, the average of the first four numbers is $4$ and that of the last four numbers is also $4 .$ If the average of all the seven numbers is $3,$ then fourth number is?

The average of three numbers of which greatest is $16$ is $12 .$ If the smallest is half of the greatest the remaining number is

The average age of students of a class is $15.8$ $years.$ The average age of boys in the class is $16.4\, years$ and that of the girls is $15.4 \,years.$ The ratio of the number of boys to the number of girls in the class is

Of the three numbers, the first is twice the second and the second is thrice the third. If the average of the three numbers is $10,$ the numbers are