Question

Two thin lenses of power +2.5d and -1.5d are placed in contact find the power and focal length of the lens combination

Answer 1

the lens combination will be

let p1=+2.5

let p2=-1.5

1/f=p1

f=1/p1

f=1/2.5*100

f=40m

f=1/p2

f=1/-1.5*100

f=66.6

Answer 2

UR ANSWER IN THE ABOVE PIC