Using proportions, it is found that Charlotte should ask for $62.5 in the budget to spend on thread.
What is a proportion?
A proportion is a fraction of a total amount, and the measures are related using a rule of three. Due to this, relations between variables, either direct(when both increase or both decrease) or inverse proportional(when one increases and the other decreases, or vice versa), can be built to find the desired measures in the problem, or equations to find these measures.
Each uniform needs 50 buttons, and there are 100 uniforms, hence the number of buttons needed is:
50 x 100 = 5000.
Each button requires of a yard of thread, hence the number of yards needed is:
5000 x 1 = 5000 yards.
A 400-yard spool of thread is sold for $5, hence the budget needed is:
(5000/400) x 5 = $62.5.
More can be learned about proportions at https://brainly.com/question/24372153
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