You just finished some yard work for your eccentric neighbor, Mr. Grimes. He prepares some lemonade for you while you rest at his kitchen table.
“Thank you for your help today,” he says as he places two envelopes on the table in front of you. “Both envelopes contain money. Pick one and you can keep the money inside.” As you reach for one of the envelopes he adds, “One envelope has exactly twice the amount of money as the other.”
You pick one of the envelopes and open it. Inside you find a $20 bill. You are about to pocket the money when Mr. Grimes interjects, “I’ll give you a chance to switch envelopes if you’d like.”
Should you switch envelopes?