In a department $10\%$ of the staff have a salary of $\$20,000, 30\%$ a salary of $\$25,000, 50\%$ a salary of $\$30,000, 10\%$ a salary of $\$40,000$. What is the average salary?

Question

( A ) 28500
( B ) 30000
( C ) 29500
( D ) 30500