18. 12/4 =3, 36/12 =3 the ratio is 3
19. 108/162 =0.667, 72/108= 0.667 the ratio is 0.667 or 2/3
20. 2/3 / 4/3 = 1/2, 1/3 /2/3 = 1/2, the ratio is 1/2
