Answer:
20 tickets.
Explanation:
Given:
After selling 200 tickets, they made a profit of $12,000.
Question asked:
How many more tickets it must be sold by charity to cover the cost of $1,200 ?
Solution:
First of all we will calculate profit earned by selling 1 ticket.
By unitary method:
After selling 200 tickets, they made a profit = $12,000.
After selling 1 ticket, they made a profit =

Now, we have to find number of more tickets must be sold to cover to cost of $1200.
It is clear that cost must be cover by earning profits, so to earn $1200 as profit we have to sell number of tickets:-
By unitary method:
Amount of profit must be earned divided by profit earned from each ticket,

Therefore, they had to sell 20 more tickets to cover necessary cost of $1,200.