**Given:** |R_{1}| : |R_{2}| = 1 : 5, u = -15 cm,

v = +7.5 cm, n = 2

**To Find:** Radii of curvature of double convex lens (R_{1}) and (R_{2})

**Formula:**

**Calculation: **From formula (i),

\(\frac{1}{f}=\frac{1}{7.5}-\frac{1}{(-15)}=\frac{1}{5}\)

∴ f = +5 cm

Substituting this value in formula (ii), we get,

By sign conventions,

Substituting in equation (1),

∴ R_{1} = 6 cm

Using in equation (2),

R_{2} = 5 × 6 = 30 cm