set them in order then start canceling out from both sides until you reach the middle .. so you'll have it like this: 5,5,7,10,13, 15,15 15,20, 25
then you cancel out 25 with 5 then 20 with the second 5 and so on until you end up with 13 and 15 in the middle with means you'll have to get their average since you can't cancel them out . doing this you'll end up with 13+15/2 = 14 and that's your answer !
