Answer:
0.046 m
Explanation:
The lens equation states that:
[tex]\frac{1}{f}=\frac{1}{p}+\frac{1}{q}[/tex]
where
f is the focal length
p is the distance of the object from the lens
q is the distance of the image from the lens
For this problem, we have
p = 4.0 m (distance of Betty and Ahmed from the lens)
f = 0.045 m (focal length of the lens, which is positive since it is a converging lens)
So we can re-arrange the formula to find q
[tex]\frac{1}{q}=\frac{1}{f}-\frac{1}{q}=\frac{1}{0.045}-\frac{1}{4.0}=21.97m^{-1}\\f=\frac{1}{21.97}=0.046 m[/tex]
