Step 1: Use the average price formula.
We are given that the total number of tickets sold is 1000, and the average price of the ticket sold is \$42. The price of adult tickets is \$50, and the price of children’s tickets is \$30.
Let the number of children’s tickets sold be \( x \), and the number of adult tickets sold be \( 1000 - x \).
Step 2: Set up the equation for the average price.
The total price of tickets sold is the sum of the prices of adult and children’s tickets:
\[
50(1000 - x) + 30x = 42 \times 1000
\]
Step 3: Simplify the equation.
\[
50(1000 - x) + 30x = 42000
\]
\[
50000 - 50x + 30x = 42000
\]
\[
50000 - 20x = 42000
\]
\[
-20x = 42000 - 50000
\]
\[
-20x = -8000
\]
\[
x = \frac{-8000}{-20} = 400
\]
Step 4: Conclusion.
The number of children’s tickets sold is 400. So, the correct answer is (C) 400.