That math question you reblogged is part of a larger worksheet, teaching kids how to do mental math easier and quicker, not how to do addition. You "make 10" when adding 8 + 5 by adding to an easier number (10). THEN you add on the 3 to get the solution. This can be applied to larger numbers like 6204 plus 5930. You know 6000 + 5000 = 11000 and you "make" the next easiest number by adding 200 + 900, which gives you 12100, then add 30 + 04 to make 34. Tack it on and wala, the answer is 12134.