What number lies halfway between 0.18 and 0.2?

To find the number halfway between two values, you can calculate the average of the two values. In this case, the average of 0.18 and 0.2 is (0.18 + 0.2) / 2 = 0.19. Therefore, the number halfway between 0.18 and 0.2 is 0.19.