the focal length of a concavo-convex lens of radius of curvature 5 cm and 10cm is 20cm. what will be its focal length in water.? given ^{a}µ_{w} = 4/3 .

ive tried solving this but my answer is incorrect, i have a bit of problem with questions like this, like plano-convex , convexo-concave , because i cant understand what sign conventions to use with these, tho the ones i solved before gave correct answres, i just cant get this one right!

thanks to anyone offering help!

if anyone has a site url which can help me with questions involving two lenses, i'd really appreciate it!

thanks again!

rosala Feb 7, 2019