After my usual job, at afternoon, this week is fully dedicated to exercise math with my son. Next week he will have a competition...so...I'm not bored :) The following is an exemple of task:

In the O+OS+OSI equation the same letters means the same numbers, the result of ecuation is a triple digit number and the letter "O" can't be zero. How much is the difference between the highest possible and the smallest possible number :)

(this task is for 2nd class kids, ~8-9 years) Enjoy it! ;)