Let's denote the number of adults as \( a \) and the number of children as \( c \). We have two equations based on the information provided:
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The total number of people attending is 500: \[ a + c = 500 \]
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The total earnings from admission charges should be $3,500: \[ 10a + 5c = 3500 \]
Now we can solve these equations simultaneously.
First, let's solve the first equation for \( c \): \[ c = 500 - a \]
Next, we can substitute this expression for \( c \) into the second equation: \[ 10a + 5(500 - a) = 3500 \]
Expanding this gives: \[ 10a + 2500 - 5a = 3500 \]
Combining like terms: \[ 5a + 2500 = 3500 \]
Now, subtracting 2500 from both sides: \[ 5a = 1000 \]
Dividing by 5 gives: \[ a = 200 \]
Now that we have the number of adults, we can find the number of children using the equation \( c = 500 - a \): \[ c = 500 - 200 = 300 \]
Thus, the PTA needs:
- 200 adults
- 300 children
So the final answer is: 200 adults; 300 children.