What is the nearest 100 of 77?

The rule when rounding off numbers is "If the first figure to be discarded is 5 or more then the previous figure is increased by 1".

As the nearest 100 is required then regard 77 as 077.

The first number to be discarded is 7 and as this is greater than 5 then the previous number (which is 0) is increased by 1.

So 77 rounded to the nearest 100 becomes 100.