Five machines a day, each harder. Feed one a number from 0 to 99 to see what comes out. Then take the exam: it shows a new number, you say what comes out. The first test is free (two on the last two machines). After that each test costs 100 points. You get two tries at the answer; the second is worth half. Rules use everyday arithmetic: adding, multiplying, remainders, digits, odd and even. There is a calculator beside the keypad for working things out.