Twot thin lenses when placed in contact,...

Twot thin lenses when placed in contact, then the power of combination is +10D. If they are kept 0.25m apart, then the power reduceds to +6D. The focal lengths of the lenses (in m) will be

(5 cm, 50 cm)

(10 cm, 40 cm)

(20 cm, 30 cm)

(12.5 cm, 50 cm)

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