Question

${\Huge{\mathbb{QUESTION}}}$
A 10mm long alpin is placed vertically in front of a concave mirror. A 5mm long image of alpin is formed at a distance of 30 cm in front of the mirror. The focal length of this mirror is ____________
(a) - 30 cm
(b) - 20 cm
(c) - 40 cm
(d) - 60 cm


{Give answer's with explanation and do not even think to give irrelevant answers otherwise on the spot it will be reported.}
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Answer 1

Answer:

- 20 is the right answer of this question

Answer 2

Answer:

option (b) -20 is right answer ok..