i hate fractions ​

 There are only two ways of getting $25.....chose a $5 bill the first time  and a $20 bill the second time....or   vice-versa

So.....the total probability is   (2 /11) * (4/11)  +  (4/11) (2/11)   =   8/121  + 8/121    =   16 / 121