Someone actually me i don't get this

#13 isn't too bad my friend. Just do 21-9, then divide by 4. So each ticket was $3. 
15 is similar too. so he has 9 more than half. Take 9 away from 21, and you have 12. Double that, and you have the original 24.

Ifound this on google “a skewed (non-symmetric) distribution is a distribution in which there is no such mirror-imaging. a "skewed right" distribution is one in which the tail is on the right side. a "skewed left" distribution is one in which the tail is on the left side. the above histogram is for a distribution that is skewed right.” i hope this you for what your looking for