When estimating, compatible numbers are numbers that are close in value to the actual numbers, and which make it easy to do mental arithmetic.
The answer to one would be 25534
If the number you are rounding is 5, 6, 7, 8, or 9, it goes to ten. If the numbers are 4, 3, 2, or 1, then round down. For example,, 37 is rounded to 40. 34 is rounded to 30.