This is another problem from Dan Griller.
“In the triangle ABC, CN and MB are straight lines, ÐCAB = 90° and CM = MA = AN = NB = 5. Find the exact area of the shaded region.”
See the Triangle Bow-tie Problem for a solution.
Shortest Pyramid Path
This is an earlier puzzle from Presh Talwalkar.
“A square pyramid has base PQRS and vertex O. Each edge has length equal to 20. Calculate the shortest distance along the outer surface of the pyramid from P to T, the midpoint of OR.”
See Shortest Pyramid Path for solutions.
Another Boat Puzzle
This is another typical travel puzzle from the 2024 Math Calendar.
“A boat travels downriver at 30 mph, then goes back up along the same path at 20 mph. What is the boat’s average speed?”
As before, recall that all the answers are integer days of the month.
See Another Boat Puzzle for a solution.
Donkey Riding
This is a simple 1917 puzzle from Henry Dudeney.
“During a visit to the seaside Tommy and Evangeline insisted on having a donkey race over the mile course on the sands. Mr. Dobson and some of his friends whom he had met on the beach acted as judges, but, as the donkeys were familiar acquaintances and declined to part company the whole way, a dead heat was unavoidable. However, the judges, being stationed at different points on the course, which was marked off in quarter-miles, noted the following results:—The first three-quarters were run in six and three-quarter minutes, the first half-mile took the same time as the second half, and the third quarter was run in exactly the same time as the last quarter. From these results Mr. Dobson amused himself in discovering just how long it took those two donkeys to run the whole mile. Can you give the answer?
See Donkey Riding for solutions.
Lunchtime at the Fish Pond
This is a problem from the 629 AD work of Bhaskara I, a contemporary of Brahmagupta.
“A fish is resting at the northeast corner of a rectangular pool. A heron standing at the northwest corner spies the fish. When the fish sees the heron looking at him he quickly swims towards the south (in a southwesterly direction rather than due south). When he reaches the south side of the pool, he has the unwelcome surprise of meeting the heron who has calmly walked due south along the side and turned at the southwest corner of the pool and proceeded due east, to arrive simultaneously with the fish on the south side. Given that the pool measures 12 units by 6 units, and that the heron walks as quickly as the fish swims, find the distance the fish swam.”
See Lunchtime at the Fish Pond for a solution.
Astronomical Sum
This is a problem from the 2000 Olymon (the Mathematics Olympiads Correspondence Program) for secondary students sponsored jointly by the Canadian Mathematical Society and the Mathematics Department of the University of Toronto.
Find the value of S.”
See Astronomical Sum for solutions.
Stacked Rhombuses Puzzle
This is a puzzle from Talwalkar’s set of “Impossible Puzzles with Surprising Solutions.”
“Call this puzzle the leaning tower of rhombi.
There are 5 isosceles triangles, aligned along their bases, with base lengths of 12, 13, 14, 15, 16 cm. The 10 quadrilaterals above are in rows of 4, 3, 2, and 1. Each quadrilateral is a rhombus, and the top of the tower is a square. What is the area of the square?”
See Stacked Rhombuses Puzzle for solutions.
A Simple Plan
This is a slightly stimulating thought puzzle from Futility Closet.
“You have three identical bricks and a ruler. How can you determine the length of a brick’s interior diagonal without any calculation?”
See A Simple Plan
Evaporating Pool Problem
This is a fairly straight-forward problem from A+ Click.
“The water from an open swimming pool evaporates at a rate of 5 gallons per hour in the shade and 15 gallons per hour in the sun. If the pool loses 8,400 gallons in June and there were no clouds, what is the average duration of night during that month?”
Answer Choices: 6 hours 8 hours 10 hours 12 hours
See Evaporating Pool Problem for solutions.
Curious Calendar Puzzle
This is a curious relation from the 2024 Math Calendar.
“10! seconds is exactly how many weeks?”
As before, recall that all the answers are integer days of the month, and also recall that 10! = 10x9x8x … x3x2x1.
See a Curious Calendar Puzzle for a solution.