Tidy Numbers

At Maths time in the group that I'm in is learning about Tidy numbers. To do it is you either add or Take away a number. I add did one more to the 49 to make 50 then I added 25, and it made 75.  I took away 1 and that made 74. If we add the number we use the other number to add to the number, we add the numbers that we either take away or add. Tidy numbers are an easier way to add or subtract. Have you ever done this? If you did what was the number?