Varsity Math 112


A medicinal puzzle and a shopping puzzle are on this week’s workout menu.



Precise Prescription

The coach poses a medical challenge to the team: A doctor must measure out a precise fraction of a tablet for a young patient. She has an empty 5-ounce vial, an empty 3-ounce vial, a water supply, a sink, and a single water-soluble tablet. 

How can she measure out a dose (dissolved in water) of exactly 10% of a tablet?

Gift Dilemma

Math team members Mandy and George want to buy a DVD set for the coach, and each has a positive whole number of dollars. Mandy finds that she is $2 shy of the price; George finds that he is $32 shy. If they pool their money, they still don’t have enough to buy the DVD set.

How much is the DVD set if it costs a whole number of dollars?


Solutions to week 111

The total number of Pumpkins in the Crop was 42 + 50 + 75 = 167. The solution to The Halloween Goblin is 46. With the proper strategy, all but the first person goes free.

Pumpkin Crop answer explained: Let the weight of the total crop be W. The 42 lightest pumpkins weigh an average of .25W/42 each and the 50 heaviest pumpkins weigh an average of .30W/50 each. Thus, the remaining n pumpkins weigh .45W and the average weight of each of those pumpkins must be .45W/n. This must not be less than .25W/42 nor more than 30W/50. This leads uniquely to n = 75 so the total number of pumpkins in the crop was 75 + 42 + 50 = 167.

The Halloween Goblin answer explained: What is needed is agreement from all that whoever goes first will be a martyr. All of you agree on an ordering of cards that labels the full deck from 0 to 51. The martyr adds the numbers of the cards he or she can see and takes the result modulo 52 (divide the sum by 52 and take the remainder). Call this result R. The martyr guesses the card corresponding to R. Each other person then knows that the sum of cards they see, leaving out the card from the martyr, will equal R if their card is added in. Each person other than the martyr deduces their card and is set free.

Recent Weeks

Week 111: Pumpkin Crop & The Halloween Goblin, solutions to Making 25 & Two Ways to 32

Week 110: Making 25 & Two Ways to 32, solutions to Commuters’ Dilemma & Construction Conundrum

Week 109: Commuters’ Dilemma & Construction Conundrum, solutions to Nine Coins & Five Questionable Coins

Week 108: Nine Coins & Five Questionable Coins, solutions to Ten from Two & Triangular Boundary

Week 107: Ten from Two & Triangular Boundary, solutions to Simple Multiple & Small and Simple

Links to all of the puzzles and solutions are on the Complete Varsity Math page.

Come back next week for answers and more puzzles.