N can be the product of C and D. Note that both C and D are greater than 0.5, but smaller than 1. The product of two numbers greater than 0.5 must be greater than 0.5*0.5=0.25, so M (0.25) is too small. However, the product must also be smaller than C, since C is multiplied by a number D less than 1. N is the only point on the number line between M and C.