Refractive index of a glass convex lens is $1.5$. The radius of curvature of each of the two surfaces of the lens is $20 \text{ cm}$. The ratio of the power of the lens when immersed in a liquid of refractive index $1.25$ to that when placed in air is
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The power of a lens is directly proportional to $(\mu_{rel} - 1)$. Use this to quickly find the ratio without calculating individual powers.