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# What should be the focal length of a simple magnifying lens so that it magnifies 10 times and the image is formed 25 cm from the eye.

$(a)\;25 \;mm \\ (b)\;25\;cm \\ (c)\;10\;mm \\ (d)\;10\;cm$

magnification for simple lens is
$m= 1+\large\frac{D}{fe}$
$10=1+\frac{25}{fe}$
$f_e =\large\frac{25}{9}$
$\qquad= 25 mm$
Hence a is the correct answer.