S2 Sampling Distribution Median

Hi guys so this question is getting on my nerves - I can't see how they get the median probability for 20? I have done all of the possible combinations and I still get 56/125? I have got (20,20,20), 3(20,20,50), 3(10,20,20), 3(10,20,50) and there's still more apparently, maybe it's an obvious one but I can't seem to get it?

cheers




Posted from TSR Mobile

The list seems complete as regards the values of the coins, although it should be 6(10,20,50)

How comes?

Number of arrangements of 3 distinct objects = 3! = 6

a,b,c
a,c,b
b,c,a
b,a,c
c,a,b
c,b,a.