Cameras and optics?

A camera is focused on a group of people, 10.00m distant from the lens, which has a focal length of 35.00mm. Under these conditions:
a) What is the lens to film distance?
b) What is the magnification?
c) What is the maximum height of a person whose image can completely fit on the film, if the film height is 0.0240m?

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I tried to do this question, cause there is a similar example in my textbook, and I got really small numbers which makes me think that I did it wrong. I used the 1/F = (1/Di) + (1/Do) equation. Any help would be appreciated!

I think you were using the correct equation, so you probably got the correct answers. Just make sure all the distances are in the same units.

a) using your equation I got 35.1229 mm. The answer should be a little greater than the focal length since the object is not at infinity, but is many focal lengths away.

b) The magnification is just the ratio of image distance to object distance. Therefore I get the magnification to be

m = 35.1229/10000 = 0.00351229 which is probably the small number you are concerned about

c) the max height would be the max image size divided by the magnification or

0.024/0.00351229 = 6.83315 meters

I hope this helped.