Q .     The plano-convex lens of focal length 20 cm
and 30 cm are placed together to form a double
convex lens. The final focal length will be :

BITSAT 2006
A

12 cm

B

60 cm

C

20 cm

D

30 cm

HINT

Equivalent focal length `1/F = (1/f_1) + (1/f_2)`
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