The answer depends on the context.
If considering the 1877 + 11 then a compatible number would be 1880
but
if considering 1877 + 11,000,000,000,000,000 the compatible number is 0.
540
A compatible number for 260 is 300. This is because 300 is a rounded number that is close to 260, making it easier to perform mental calculations, especially in addition or subtraction. Using compatible numbers like 300 can simplify estimating sums and differences.
12.5577
A compatible number close to 12 is 10. It is easier to work with when performing mental calculations, and it rounds down to a nearby, simpler figure. Another option is 15, which rounds up, making it useful for estimating totals or simplifying division.
it makes it easier when u round
540
A compatible number for 260 is 300. This is because 300 is a rounded number that is close to 260, making it easier to perform mental calculations, especially in addition or subtraction. Using compatible numbers like 300 can simplify estimating sums and differences.
12.5577
19.8889
A compatible number close to 12 is 10. It is easier to work with when performing mental calculations, and it rounds down to a nearby, simpler figure. Another option is 15, which rounds up, making it useful for estimating totals or simplifying division.
it makes it easier when u round
11
It is 0.7*600 = 420
Rounding, you see the number and just make it look neater or easier to use. Estimating, you guess a number.
It is a compatible number
As a Roman numeral 1877 is MDCCCLXXVII
Rounding is going to the nearest tens, hundreds, thousands etc., depending on the problem. Compatible numbers are numbers the work well with each other. Both of these are estimating.