Answer: At least 1125 race entries
In other words, there needs to be 1125 or more entries
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Work Shown:
x = number of race entries
The charity gets $55 per race entry
1 entry = 55 dollars donated
x entries = 55x dollars donated
This is ignoring the fact that "it must spend $15 per race entry to cover the cost of the race."
If we include this cost, then they're really pulling in 55-15 = 40 dollars per entry.
So we have to update the 55x into 40x
Add this onto the 10,000 in donations they get elsewhere
We have the expression 40x+10,000
We want this to be at least 55,000
So we want 40x+10,000 to be 55,000 or larger
We can say the following
![40x + 10,000 \ge 55,000\\\\40x \ge 55,000 - 10,000\\\\40x \ge 45,000\\\\x \ge 45,000 / 40\\\\x \ge 1,125\\\\](https://img.qammunity.org/2021/formulas/advanced-placement-ap/high-school/474it2gilwfyxr4cadtromxqae9b5entsr.png)
This means there needs to be at least 1125 race entries.