The average of $30$ numbers is $15 .$ The average of the first $18$ numbers is $10$ and that of the next $11$ numbers is $20 .$ The last number is

Of the three numbers, the average of the first and the second is greater than the average of the second and the third by $15 .$ What is the difference between the first and the third of the three numbers?

Visitors to a show were charged $Rs.\,15.00$ each on the first day, $Rs.\, 7.50$ on the second and $Rs.\, 2.50$ on the third day. Visitors total attendance for three days were in the ratio $2: 5: 13$ . Find out the average charge per visitor for the entre show. (in $Rs.$)

A club has $15$ men and $25$ women. The average age of men is $10\, years$ and the average age of women is $12 \,year.$ What is the average age of the whole club in $year$?

The sum of five consecutive integers is $a$ and the sum of next five consecutive integers is $b$. Then $\frac{(b-a)}{100}$ is equal to

In a class of $100$ students, the mean marks obtained in a subject is $30$ and in another class of $50$ students the mean marks obtained in the same subject is $60 .$ The mean marks obtained by the students of two classes taken together is