This week, I’ll continue with some more problems from the contests for the 2014 conference of the International Group for Mathematical Creativity and Giftedness. We’ll look at problems from the Intermediate Contest today. Recall that the first three problems on all contests were the same; you can find them here.
The first problem I’ll share is a “ball and urn” problem. These are a staple of mathematical contests everywhere.
You have 20 identical red balls and 14 identical green balls. You wish to put them into two baskets — one brown basket, and one yellow basket. In how many different ways can you do this if the number of green balls in either basket is less than the number of red balls?
Another popular puzzle idea is to write a problem or two which involve the year of the contest — in this case, 2014.
A positive integer is said to be fortunate if it is either divisible by 14, or contains the two adjacent digits “14” (in that order). How many fortunate integers n are there between 1 and 2014, inclusive?
The other two problems from the contest I’ll share with you today are from other contests shared with me by my colleagues.
In the figure below, the perimeters of three rectangles are given. You also know that the shaded rectangle is in fact a square. What is the perimeter of the rectangle in the lower left-hand corner?
I very much like this last problem. It’s one of those problems that when you first look at it, it seems totally impossible — how could you consider all multiples of 23? Nonetheless, there is a way to look at it and find the correct solution. Can you find it?
Multiples of 23 have various digit sums. For example, 46 has digit sum 10, while 8 x 23 = 184 has digit sum 13. What is the smallest possible digit sum among all multiples of 23?
You can read more to see the solutions to these puzzles. Enjoy!