On the first day of the school year, a geography teacher was
murdered. The police had 4 suspects: the gardener, the math
teacher, the coach, and the school principal. They all had
alibis:
The gardener was cutting bushes.
The math teacher was holding a mid-year test.
The coach was playing basketball.
The principal was in his office.
The killer was arrested immediately. Who killed the
geography teacher, and how did the police solve the
mystery?
X+y=