Let x be the value of the third term. Since it's a geometric sequence, then: Third term/Second term = Fourth term/Third term x/20 = 11.25/x Cross multiplication: x^2 = 225 x = 15 So since the ratio is constant, then it is x/20 = 15/20 = 3/4 So the common ratio is 3/4 or 0.75.
