Because we can reproduce with just one and if more eggs were released, the female reproductive life (which is 40 years) would be shorter and so there would be less time for every female human to reproduce since the amount of eggs is limited. (Also fraternal twins come from 2 eggs released at the same time)
Answer:
The focal length of the lens should be -51.5 cm (a concave lens).
Explanation:
The purpose of the lens is to make objects at 48.5 cm appear at the healthy near point. The healthy near point is 25.0 cm.
We use the lens formula

where <em>f</em> = focal length, <em>u</em> = object distance and <em>v</em> = image distance.
In this case, <em>u</em> = 48.5 cm and <em>v</em> = -25.0 cm.
<em>v</em> is negative because the image is virtual an not real. (Here, we are using the real-is-positive sign convention)


The negative sign indicates the lens is concave.