In the sum $\otimes + 1\otimes + 5\otimes + \otimes\otimes + \otimes1 = 1\otimes\otimes$ for which digit does the symbol $\otimes$ stand?

How many pairs of natural numbers are there such that the difference of whose squares is 63?

Consider the following data:

For which period was the natural growth rate maximum?

How many different 5-letter words (with or without meaning) can be constructed using all the letters of the word ‘DELHI’ so that each word has to start with D and end with I?

A shop owner offers the following discount options on an article to a customer:

1. Successive discounts of $10\%$ and $20\%$, and then pay a service tax of $10\%$.
2. Successive discounts of $20\%$ and $10\%$, and then pay a service tax of $10\%$.
3. Pay a service tax of $10\%$ first, then successive discounts of $20\%$ and $10\%$.

Which one of the following is correct?

How many different sums can be formed with the denomination Rs. 50, Rs. 100, Rs. 200, Rs. 500, and Rs. 2,000 taking at least three denominations at a time?