Distance between an object and three times magnified real image is 40 cm . The focal length of the mirror used is 
cm.
A
B
-15
C
-10
D
-20
Text Solution
Verified by ExpertsThe correct answer is:
B
For a mirror with magnification 
(real image), object and image distances satisfy 
.
Since 
, we have 
, giving 
, so 
and 
.
Using mirror formula: 
Hence 
.
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