From the 2003 Flanders Junior Maths Olympiad:
To play soccer with three people, two field players try to score past the player in goal, and whoever scores stands in goal for the next game. Arne, Bart and Cauchy play the game, with A playing 12 times on the field, B playing 21 times on the field, and C playing 8 times in goal.
Who scored the 6th goal?
Here is a problem of my own invention; I hope you enjoy it:
At a festival, every guest presented a gift to every older guest. The ten youngest guests combined gave thirteen times as many gifts as they received. What was the total number of gifts presented at the festival?
From the 2014 American Invitational Maths Examination:
The repeating decimals 0.ababab… and 0.abcabc… satisfy
0.ababab… + 0.abcabc… = 33/37.
Find the digits a, b and c.
From the 2008 Netherlands Junior Maths Olympiad:
A hexagon has six angles all equal to 120 degrees. The lengths of four consecutive sides are 2000, 2006, 2008 and 2009. Determine the perimeter of the hexagon.
Here I present my first entry into the Vault, a collection of puzzles so well crafted, they provide the standard by which all other problems should be measured.
From the 1992 Tournament of the Towns:
Let n be a positive integer. Prove that there is a multiple of n, the sum of whose digits is odd.
Today I worked through the final five problems from the 2010 AMC10 Paper A, an American Maths Challenge. It was the very last problem that turned out to be my favourite:
Jim starts with a positive integer n and creates a sequence of numbers. Each successive number is obtained by subtracting the largest possible integer square less than or equal to the current number, until zero is reached. For example, if Jim starts with n = 55, then his sequence contains five numbers: 55, 6, 2, 1, 0.
What is the smallest value of n for which his sequence contains eight numbers?
From the 2013 Pink Kangaroo:
Yurko saw a tractor slowly pulling a long pipe down the road. Yurko walked along beside the pipe in the same direction as the tractor, and counted 140 paces to get from one end to the other. He then turned around and walked back to the other end, taking only 20 paces. The tractor and Yurko kept to a uniform speed, and Yurko’s paces were all 1 metre long.
How long was the pipe?