Round off the number 690 to nearest 100.
(a) 780
(b) 690
(c) 700
(d) 800

Hint: In this question, we will use the concept of rounding off by comparing it to 50 to round off the given number to the nearest hundred.

Complete step-by-step answer:
When we round off a number to nearest 100, we find that number which is a multiple of 100 and is nearer to the given number than any other multiple of 100.
For this, if the tens and ones place digit of given number together form a number greater than or equal to 50, then we change the number at hundreds place by its succeeding number and all other digits at lower places by zeroes. And, if the tens and ones place digit of given number together form a number less than 50, then we do not change the number at hundreds place but replace all digits at lower places by zeroes.
Now, in the given question, the number to be rounded off to nearest 100 is 690.
Here, digits at tens and ones place together form a number 90.
We have 90>50.
So, the digit at hundreds place, which is 6, will be replaced by its succeeding digit, which is 7. Also, all other digits which are at lower places will be replaced by zeroes.
Hence the number 690 after rounding off to 100 will be 700.
Therefore, the correct answer is option (c).

Note: In this type of questions, you must see that if you are to round off to nearest 100 then all lower places will be zeroes. So the first two options will directly be rejected. Then you can check the right option from the remaining options.