The radius of curvature of each surface of a convex lens having refractive index \( 1.8 \) is \( 20 \, \text{cm} \). The lens is now immersed in a liquid of refractive index \( 1.5 \). The ratio of power of lens in air to its power in the liquid will be \( x : 1 \). The value of \( x \) is __________.
