Points A, B, C, and D lie on a line such that AB = 4AD = 9BC. A point is selected at random between A and B. What is the probability that it is between C and D?

AB= 4AD = 9BC

AB/ 4 = AD

AB/ 9 = BC

So

AB/4 + AB/9 = AD + BC

[ 13/36]AB = AD + BC

CD = AB- [13/36]AB = 23/36 AB

So....the probabi;ity is 23/36