This problem posted by Presh Talwalkar offers a variety of solutions, but I didn’t quite see my favorite approach for such problems. So I thought I would add it to the mix.
“Thanks to Nikhil Patro from India for suggesting this! What is the sum of the corner angles in a regular 5-sided star? What is a + b + c + d + e = ? Here’s a bonus problem: if the star is not regular, what is a + b + c + d + e = ?”
See Star Sum of Angles for solutions.
This was a nice geometric problem from Poo-Sung Park @puzzlist posted at the Twitter site #GeometryProblem.
“Geometry Problem 65: Given one square leaning on another, what is the ratio of the triangular areas A:B?”
See the Leaning Squares for a solution.
This is another UKMT Senior Challenge problem, this time from 2006.
“A toy pool table is 6 feet long and 3 feet wide. It has pockets at each of the four corners P, Q, R, and S. When a ball hits a side of the table, it bounces off the side at the same angle as it hit that side. A ball, initially 1 foot to the left of pocket P, is hit from the side SP towards the side PQ as shown. How many feet from P does the ball hit side PQ if it lands in pocket S after two bounces?”
Pool Partiers should have no difficulty solving this.
See More Pool for solutions.
Normally I don’t care for combinatorial problems, but this problem from Chalkdust Magazine by Matthew Scroggs seemed to bug me enough to try to solve it. It took me a while to see the proper pattern, and then it was rather satisfying.
“You start at A and are allowed to move either to the right or upwards. How many different routes are there to get from A to B?”
See the Chalkdust Grid Problem for a solution.
The following is a famous problem of Bachet as recounted by Heinrich Dörrie in his book 100 Great Problems of Elementary Mathematics:
“A merchant had a forty-pound measuring weight that broke into four pieces as the result of a fall. When the pieces were subsequently weighed, it was found that the weight of each piece was a whole number of pounds and that the four pieces could be used [in a balance scale] to weigh every integral weight between 1 and 40 pounds [when we are allowed to put a weight in either of the two pans]. What were the weights of the pieces?
(This problem stems from the French mathematician Claude Gaspard Bachet de Méziriac (1581-1638), who solved it in his famous book Problèmes plaisants et délectables qui se font par les nombres, published in 1624.)”
The problem has a nice solution using ternary numbers.
See the Weight Problem of Bachet for a solution.
(Update 4/10/2019) Continue reading
This is a fun little problem from the United Kingdom Mathematics Trust (UKMT) Senior Math Challenge of 2008.
“What is the remainder when the 2008-digit number 222 … 22 is divided by 9?”
(Hint: See The Barrel of Beer)
See A Multitude of 2s for a solution.
This is an interesting problem from the United Kingdom Mathematics Trust (UKMT) Senior Math Challenge of 2008.
“The length of the hypotenuse of a particular right-angled triangle is given by √(1 + 3 + 5 + … + 23 + 25). The lengths of the other two sides are given by √(1 + 3 + 5 + … + (x – 2) + x) and √ (1 + 3 + 5 + … + (y – 2) + y) where x and y are positive integers. What is the value of x + y?”
See the Right Triangle with Roots for a solution.
This turns out to be a fairly challenging driving problem from Longley-Cook.
“Mileage on the Thru-State Turnpike is measured from the Eastern terminal. Driver A enters the turnpike at the Centerville entrance, which is at the 65-mile marker, and drives east. After he has traveled 5 miles and is at the 60-mile marker, he overtakes a man operating a white-line painting machine who is traveling east at 5 miles per hour. At the 35-mile marker he passes his friend B, whose distinctive car he happens to spot, driving west. The time he notes is 12:20 p.m. At the 25-mile marker he passes a grass cutter traveling west at 10 miles per hour. A later learns that B overtook the grass cutter at the 21-mile marker and passed the white-line painter at the 56-mile marker. Assuming A, B, the painter and the grass cutter all travel at constant speeds, at what time did A enter the turnpike?”
See Turnpike Driving for a solution.
Here is another Presh Talwalkar problem that seems unsolvable at first glance.
“Every day, a train passes a train station along a straight line track, and the train moves at a constant speed. Two friends, A and B, want to determine how long the train is. Lacking proper equipment, they devise the following method. They first synchronize their walking. Both A and B walk at the same constant speed, and each step they take is the same length. One day they line up back to back at the train station. When the front of the train reaches them, they both start walking in opposite directions. Each person stops exactly as the back of the train passes by. If person A takes 30 steps, and person B takes 45 steps, how long is the train, in terms of steps?”
See the Train Length Puzzle for a solution.
This is a great puzzle by H. E. Dudeney involving a very useful technique.
“A man bought an odd lot of wine in barrels and one barrel containing beer. These are shown in the illustration, marked with the number of gallons that each barrel contained. He sold a quantity of the wine to one man and twice the quantity to another, but kept the beer to himself. The puzzle is to point out which barrel contains beer. Can you say which one it is? Of course, the man sold the barrels just as he bought them, without manipulating in any way the contents.”
See the Barrel of Beer for an answer.
