$3 \frac{6}{7} + 6 \frac{1}{4} - 5 \frac{1}{3} + 2 \frac{1}{2} = ?$

In a two-digit number,the digit in the unit's place is $1$ more than twice the digit in the ten's place. If the digits in the unit's place and the ten's place are interchanged,the difference between the new number and the original number is $1$ less than the original number. What is the original number?

The greatest number among $3^{50}, 4^{40}, 5^{30}$ and $6^{20}$ is

$63 + 371 \div 7 = ?$

Which one of the following is the largest prime number of three digits?

Let $x$ be the smallest number,which when added to $2000$ makes the resulting number divisible by $12, 16, 18$ and $21$. The sum of the digits of $x$ is