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
This means there needs to be at least 1125 race entries.