Puzzler Answers

Puzzler #1: The thirty dollars I already had in my wallet was in the form of fifteen two-dollar bills; subsequently, there was no point in exchanging them for other twos.

Puzzler #2: One.  A single roll of dollar coins is worth $25 dollars.  But that is cheating.  The fewest rolls of coins that add up to exactly $16.50 is 5 (there are 4 combinations of 5 rolls that work.)

#2 Bonus: If the rolls are $10 in half-dollars, $6 in nickles (three $2 rolls) and 50¢ in pennies, that is a total of 190 coins.

Puzzler #3:  The weights of silver coins were designed to be proportional to their face value.  So ten dimes weighs the same amount as four quarters.

#3 Bonus:  The same law that took all of the silver out of dimes and quarters reduced the amount of silver in half-dollars to 40%, so the last silver halves had less silver than an equal face value of earlier coins.