Finding Distance of Retina from Lens: Power from 40D to 44D

[AlchemistK]

Homework Statement

The accomodation power of a boy whose far point is at infinity can vary from 40D to 44D.
Using this data find the distance of the retina from the lens.

Homework Equations

Power of lens,P = 1/f(in meters)
f = focal length
lens formula, 1/v - 1/u = 1/f

The Attempt at a Solution

when object is at infinity,
f=1/40 = 2.5 cm
by lens formula,

1/v-(-1/\infty) = 1/2.5
=>1/v - 0 = 1/2.5
=>v=2.5 cm

thus, distance = 2.5cm

Have i done this question right? And do i have to confirm the answer by putting the object at the near point or this is enough?

 

[Dadface]

You can't double check because the question doesn't tell you what the near point is.Just to satisfy your curiosity you may wish to assume that the near point is at 25 cm,this is taken to be the average value.