There are three people in johns family, the range of their shoe size is 4. two people in the family wear shoe size 6. johns shoe size is not 6 or 10 what is it ? ?

Since the range is = to max-min. The range, in this case, is 4. If there are three people and 2 wear 6, John is not one of them. So, either John's shoe size is the max or the min. If it is the max than John's size minus 6 = 4 or John's size is 10. However, it says it can't be 10.  So 6 - John's size =4, which means John's size is 2. Hope this helps!