One morning, a 57-year-old woman walked into her kitchen and noticed a folded piece of paper stuck to the fridge. It was a note from her husband. As she began to read, her hands trembled.

“My dear wife,” it began, “You will surely understand that I have certain needs that you, being 57 years old, can no longer satisfy. I am very happy with you, and I value you as a good wife. Therefore, I hope you will not wrongfully interpret the fact that I will be spending the evening with my 19-year-old secretary at the Comfort Inn Hotel. Please don’t be upset — I shall be home before midnight.”

She stared at the note for a moment, took a deep breath, and smiled. Instead of crying or yelling, she calmly went to her desk, grabbed a pen, and wrote her own letter.

That night, when the husband returned home, he found her note on the dining table:

“My dear husband, you too will understand that I am a woman of the same age as you, and just like you, I also have certain needs you can no longer satisfy. I am spending the evening with my 21-year-old personal trainer at the Grand Hotel. Please don’t be upset — I shall be home before midnight. P.S. Being a mathematician, you will appreciate that 21 goes into 57 more times than 19 goes into 57.”

He didn’t sleep that night — but the internet has been laughing ever since.

Moral of the story: never underestimate a brilliant wife.