 PLOT: Leaven thinks she knows what the numbers mean, and tests  whether one of the three numbers she sees is prime. Even though she  is under pressure, it ought to occur to her much more quickly that  no even numbers are prime except 2. Also, she would immediately  recognize that the only prime number ending in 5 is 5. She would  also most likely know that by adding the numbers up, if they add to  3 or 9 the number is not prime as it would be divisible by the  numbers 3 or 9 respectively.