See the figure
Find the equivalent focal length of the combination shown in the figure and position of image.

Explanation

For the concave lens
`(1)/(f) =- (n-1) ((1)/(R_(1)) - (1)/(R_(2))) = ((3)/(2)-1) ((1)/(-10)-) - (1)/(10)) = (1)/(2) xx (2)/(10) = (1)/(10)`
And, `f_(n) = (R)/(2) = (10)/(2) = 5cm`
`:. (1)/(f_(eq)) = (1)/(f_(m)) -2 (1)/(f)`
`= (1)/(5) + 2xx (1)/(10) = (2)/(5), f_(eq) = 2.5cm`