Incredible Trick Puzzle

Here is another typical sum puzzle from Presh Talwalkar.

“Solve the following sums:

_____1/(1×3) + 1/(3×5) + 1/(5×7) + 1/(7×9) + 1/(9×11) =

_____1/(4×7) + 1/(7×10) + 1/(10×13) + 1/(13×16) =

_____1/(2×7) + 1/(7×12) + 1/(12×17) + … =”

The only reason I am including this puzzle is that Talwalkar gets very excited about deriving a formula that can solve sums of this type.  This gives me an opportunity to discuss the “formula vs. procedure” way of doing math.

See the Incredible Trick Puzzle

“Fermat’s Last Theorem” Puzzle

Here is a mind-numbing logic puzzle from Futility Closet.

“A puzzle by H.A. Thurston, from the April 1947 issue of Eureka, the journal of recreational mathematics published at Cambridge University:

Five people make the following statements:—

Which of these statements are true and which false?  It will be found on trial that there is only one possibility.  Thus, prove or disprove Fermat’s last theorem.”

Normally I would forgo something this complicated, but I thought I would give it a try.  I was surprised that I was able to solve it, though it took some tedious work.  (Hint: truth tables.  See the “Pointing Fingers” post regarding truth tables.)

One important note.  The author is a bit cavalier about the use of “Either …, or …”.  In common parlance this means “either P is true or Q is true, but not both” (exclusive “or”: XOR), whereas in logic “or” means “either P is true or Q is true, or possibly both” (inclusive “or”: OR).  I assumed all “Either …, or …” and “or” expressions were the logical inclusive “or”, which turned out to be the case.

See the Fermat’s Last Theorem Puzzle

Three Triangles Puzzle

This is a nice little puzzle from the late Nick Berry’s Datagenetics Blog.

“A quick little puzzle this week. (I tried to track down the original source, but reached a dead-end with a web search as the site that hosted it, a blogspot page under the name fivetriangles appears password protected, and no longer maintained). …

There are three identical triangles with aligned bases (in the original problem, it is stated they are equilateral, but I don’t think that really matters; Any congruent triangles will do, and I’m going to use isosceles triangles in my solving). If we say that one triangle has the area A, what is the area of the two shaded regions?”

See the Three Triangles Puzzle.

Close Race Puzzle

This puzzle from the Scottish Mathematical Council (SMC) Senior Mathematics Challenge seems at first to have insufficient information to solve.

“Ant and Dec had a race up a hill and back down by the same route. It was 3 miles from the start to the top of the hill. Ant got there first but was so exhausted that he had to rest for 15 minutes. While he was resting, Dec arrived and went straight back down again. Ant eventually passed Dec on the way down just half a mile before the finish.

Both ran at a steady speed uphill and downhill and, for both of them, their downhill speed was one and a half times faster than their uphill speed. Ant had bet Dec that he would beat him by at least a minute.

Did Ant win his bet?”

See the Close Race Puzzle

(Update 1/2/2023Alternative Solution from Oscar Rojas Continue reading

Four Year Anniversary

Yet another year has passed, surprisingly, with perhaps the prospect of coming out from under the shadow of the pandemic.  Again, I thought I would present the statistical pattern of interaction with the website in the absence of any explicit feedback.

Perhaps due to fatigue from the height of the pandemic students seemed to have embraced returning to inclass education and abandoned online educational activities, at least as far as my website is concerned.  Visits dropped precipitously this school year.  Combined with a diminishing supply of fresh material this may finally spell the fading of the site.  Still, I may persist if for no other reason than my own entertainment.

Anyway, here is the summary.

See Four Year Anniversary

Spiral Areas Puzzle

This is a provocative puzzle from the Maths Masters team, Burkard Polster (aka Mathologer) and Marty Ross as part of their “Summer Quizzes” offerings for 2013.

“In the picture the top curve is a semicircle and the bottom curve is a quarter circle. Which has greater area, the red square or the blue rectangle?”

See the Spiral Areas Puzzle

Fireworks Rocket

This is another physics-based problem from Colin Hughes’s Maths Challenge website (mathschallenge.net) that may take a bit more thought.

“A firework rocket is fired vertically upwards with a constant acceleration of 4 m/s2 until the chemical fuel expires. Its ascent is then slowed by gravity until it reaches a maximum height of 138 metres.

Assuming no air resistance and taking g = 9.8 m/s2, how long does it take to reach its maximum height?”

I can never remember the formulas relating acceleration, velocity, and distance, so I always derive them via integration.

See the Fireworks Rocket

Wisdom of Old

Here is another Brainteaser from the Quantum magazine.

“King Arthur ordered a pattern for his quarter-circle shield. He wanted it to be painted in three colors: yellow, the color of kindness; red, the color of courage: and blue the color of wisdom. When the artist brought in his work, the king’s armor-bearer said there was more courage than wisdom on the shield. But the artist managed to prove that the proportions of both virtues were equal. Can you tell how? (A. Savin)”

This is another relatively simple problem, though it may look a bit daunting at first.

See Wisdom of Old