# What is the focal length of the lens? given magnification and distance

1. Apr 13, 2013

### RedLego

1. The problem statement, all variables and given/known data
A biology student wishes to examine a bug at a magnificaiton of +5.00 by looking through a single lens. the student wants the image of the bug to be a distance of 25cm from the lens. what is the focal length of the lens?

2. Relevant equations
m=-d(image)/d(object)
1/f=$\frac{1}{d(object)}$+$\frac{1}{d(image)}$

3. The attempt at a solution
first i solve for distance of object, d(object), by using the first equation:
d(object) = (25x10-2)/5

then i calculated focal length by using the second equation
f = ((1/0.5) + (1/0.25))-1 = 0.041667

i dont know what im doing wrong

2. Apr 13, 2013

### technician

This is a simple magnifying glass using a converging lens.
The image is VIRTUAL....what does this mean about the image distance in the equation???