The original puzzleThree men take a hotel room priced at \$30.00. they each give \$10.00 to the desk clerk. When the owner returns, he changes the price to \$25.00, the season being over. He gives five \$1.00 bills to the clerk and tells him to reimburse the clients. The clerk gives 3 bills to the clients and keeps 2 for himself. Each client takes one of the bills. The clients have now paid \$9.00 each, a total of \$27.00. The clerk has \$2.00 in his pocket. That makes \$29.00 in all. There was \$30.00 at the beginning. What happened to the missing dollar ? The SolutionThe clients have now paid \$9.00 each, a total of \$27.00.     No problem here.The clerk has \$2.00 in his pocket. That makes \$29.00 in all.     Here is the mistake.          The \$2.00 in the clerks pocket should not be added to the \$27.00 the clients gave,               but subtracted from it, giving the \$25.00 at the front desk.Adding always seems simpler than subtracting,     the way binary is always simpler than ternary,          as we saw in other puzzles.