Two Lenses Of Powers +2.50 D And –3.75 D Are Combined To Form A Lens Combination. Determine The Focal-length Of This Combination.  

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Two lenses of powers +2.50 D and –3.75 D are combined to form a lens combination. Determine the focal-length of this combination.  


Correct option is

– 80 cm


The power of the lens combination is given by 




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