Miss Flogginum, the mathematics teacher, was humiliating three of her pupils in front of the class. From left to right, Droopy, Dimwit and Dibdib stood with their back to the class and each had a digit from 0-9 pinned to his rear end, no digit being repeated. No pupil could see his own digit but was able to peep at the other two. The idea was that each had to make a statement about the two-digit number that would remain if he were not present. "It's the square of a whole number", said Droopy. "It's a prime number", reported Dimwit. Dibdib was bolder and surprised the class with a delightful observation. "The difference between the number and that formed by reversing the digits is three times the sum of the two digits."
=3(4+
