I have a doubt in an AIEEE-level Physics question ?

I need some help with this particular question: A concave mirror of focal length f is taken.Few drops of water are sprinkled on it.The objest needle and image needle will coincide at: a) 2f b)3f/2 c) f d)2f/3 The answer is b) 3f/2 But i don't understand why because i used to think that focal... show more I need some help with this particular question:

A concave mirror of focal length f is taken.Few drops of water are sprinkled on it.The objest needle and image needle will coincide at:
a) 2f
b)3f/2
c) f
d)2f/3

The answer is b) 3f/2

But i don't understand why because i used to think that focal length of a mirror in water is the same as that in air.Now I'm confused:(

If anyone knows the answer please let me know...And a little detail would be nice too cause i honestly can't comprehend the concept behind this!
2 answers