Okay, rounding is when you take a number such as 198 and imagine that it is something easier to do math with, like 200. 200 is easier to add with because there are zeroes in the tens place and the ones place. 725 is easier to add with than 727 because the ones place digit, (5), is an easier base to use, just like zero. Using the easier numbers, 200 + 725 = 925 Using the original numbers, 198 + 727 + 925 *Because you took two pieces from the 727 and added them to 198, the four numbers in this problem are compatible. Compatible numbers are when you use numbers that are close to the original ones and make it easier to do the problem in your head. ____ In the case of 87+ 34, the simplest numbers to use would be 90 instead of 87 and 35 instead of 34. Not as easy as the first equation, but still doable. 90+35+125 or 87+34=121 ____ In the case of 222+203, the simplest substitutions are 220 and 200. 220+200=420 or 222+203=425 Hope this helps, Ahawk
