A man has a total of 200 apples divided evenly among 5 boxes. How many apples are in each box? . What are the units for your answer?
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(200 apples) / (5 boxes) = 40 apple/box

i guess that visual aids present persuasive examples to what you are presenting, some factors would be theme (does it fit with the color, information, what you are presenting), size (can you see it, is it a big enough span of data/information), and overall look of the visual aid.

hope this : )