Find the focal length of equivalent system shown in Figure.

Explanation

Here radius of curvatures of different surfaces and refractive index are given, we can calculate focal lengths of lenses by using
`(1)/(f_(1))=((3)/(2)-1)((1)/(10)+(1)/(10))=(1)/(2)xx(2)/(10)=(1)/(10)`
`(1)/(f)=(mu_(1)-1) ((1)/(R_(1))-(1)/(R_(2)))`
`(1)/(f_(2))=((6)/(5)-1)((_1)/(10)-(1)/(20))= (1)/(5)xx((-30)/(10xx20))= (-3)/(100)`
`(1)/(f_(3))=((8)/(5)-1)((1)/(20)+(1)/(20))=(3)/(50)`
Hence, equivalent focal length
`(1)/(f)=(1)/(f_(1)) +(1)/(f_(2))+(1)/(f_(3))=(1)/(10)+(-3)/(100)+(3)/(50)`
`rArr f=100//13 cm`