Final answer:
The total magnification of a microscope is calculated by multiplying the magnification of the objective lens by the magnification of the ocular lens. Therefore, if an object is 300 micrometers long and you magnify it by 40x, the length would appear to be 12 millimeters.
Step-by-step explanation:
The total magnification of a microscope is calculated by multiplying the magnification of the objective lens by the magnification of the ocular lens. For example, if an objective lens has a magnification of 40x and the ocular lens has a magnification of 10x, the total magnification would be (40x) * (10x) = 400x.
Therefore, if you have an object that is 300 micrometers long and you magnify it by 40x, the length would appear to be (300 micrometers) * (40x) = 12,000 micrometers, or 12 millimeters.