500 tickets for a concert were sold to adults and children at $4.50 and $3.00 respectively. If the total receipts were $1,987.50, how many adult tickets were sold?
Worked solution (try it first)
Let a adult tickets be sold, so 500−a children's tickets were sold.
Receipts: 4.50a+3.00(500−a)=1987.50, which is 1.5a+1500=1987.5.