Answer: Incentives.
Explanation:
Incentive is an economic term that is introduce to motivate and encourage people towards some kind of work. Incentive is an amount of money that is given to the achiever.
Here, the incentive is the amount of money allotted for prize. Student knows that entry fees is $10 each. If a student scores A grade, then the maximum amount he can get from prize is $100, which is greater than the entry fees of the contest. So, there is a incentive for the students to score grade 'A'.
Therefore, this motivate students to study well and work hard.