A student finds the average of $10$ positive integers. Each integer contains two digits. By mistake, the boy interchanges the digits of one number, say $ba$ for $ab$. Due to this, the average becomes $1.8$ less than the previous one. What was the difference between the two digits a and b?

1 USD = Rs. 67.89. A money changer adds a margin of Rs. 1.11. What will be the cost of 150 USD ? 

1. Rs. 10,183
2. Rs. 10,350
3. Rs. 10,330
4. Rs. 10,450

The sum of three consecutive numbers is $126$. Find the highest number-

1. $41$
2. $42$
3. $43$
4. $44$

Find such number, so that one fourth of the number is $8$more than $5$:

If $\mathrm{A}$ is integer, $\mathrm{B}$ is natural number then $\mathrm{B}-\mathrm{A}=?$

Twice the difference between two numbers is equal to their sum. If one number is $15$, Find the other number.

1. $15$
2. $10$
3. $5$
4. $20$

How many times does the number $3$ occur in unit's place for numbers ranging from $1$ to $100$?

1. $20$
2. $11$
3. $10$
4. $19$