Question

The third proportional to 12, 18 is​

Answer 1

The third proportional of two numbers a and b is defined to be that number c such that a : b = b : c. So you want to find a number c such that 12 : 18 = 18 : c. That number is 27. If BD = AC, then the 3rd proportional to AB and AC is CE.

Answer 2

,12:18::18:x

=>(product of extremes =product of means)

=>12×x=18×18

=>x=18×18/12

=>x=27