Professor and his wife

A college professor decides to email his wife. It said: My beloved wife, you are 64 years old. It pains me to tell you that you have not met my physical needs. So, I have decided, with some regret, to take my 18 year old secretary as a mistress. I hope you will understand.

The wife recieves the email and decides to write one of her own. She says: My dear husband, you are also 64 years old. You also have not met my physical needs. I have also decided to take on a lover, in the form of our 18 year old pool boy.

But let me remind you one thing, my husband, since you are a math professor: 18 can go into 64 more times than 64 into 18.