A student had to solve $26$ problems.His father promised that he will give him $800$ euro for every problem that we would solve correctly,but he would abstract $500$ euro for every problem that would be wrong.Finally the father estimated the correct and wrong problems and noticed that his son should not either get ,or give money.How many problems successfully solved and how many wrong?
Any ideas how to approach it?
Let $x$ be the number of problems he solved. Then $26-x$ is the number of problems he didn't solve. Then, from the task: $0=x*800-(26-x)*500$. I am sure you can continue from here.