Sure, between the spying on millions of Americans and the sitting on critical security vulnerabilities for years, the National Security Agency (NSA) has a pretty bad reputation.
But have you heard about its brain-teasers?
The US spy agency employs some of America's best and brightest as spooks and code-breakers, so it's no surprise that its employees might have an interest in riddles and puzzles.
Every month, the NSA publishes on its website a brain-teaser written by an employee that members of the public can try their hand at.
One month it's a maths challenge created by an applied research mathematician; the next it's a logic puzzle by a systems engineer. They're all published in what the NSA calls its "Puzzle Periodical."
"Intelligence. It's the ability to think abstractly. Challenge the unknown. Solve the impossible. NSA employees work on some of the world's most demanding and exhilarating high-tech engineering challenges. Applying complex algorithms and expressing difficult cryptographic problems in terms of mathematics is part of the work NSA employees do every day," the NSA says on its website.
We've rounded up a six of the most interesting brain-teasers below. So take a read, and see if you can out-smart the NSA's most fiendish riddlers!
Here's a relatively easy one to start off with, from July 2016:
Submitted by Sean A., NSA Applied Mathematician
On a rainy summer day, brothers Dylan and Austin spend the day playing games and competing for prizes as their grandfather watches nearby. After winning two chess matches, three straight hands of poker and five rounds of ping-pong, Austin decides to challenge his brother, Dylan, to a final winner-take-all competition. Dylan clears the kitchen table and Austin grabs an old coffee can of quarters that their dad keeps on the counter.
The game seems simple as explained by Austin. The brothers take turns placing a quarter flatly on the top of the square kitchen table. Whoever is the first one to not find a space on his turn loses. The loser has to give his brother tonight’s dessert. Right before the game begins, Austin arrogantly asks Dylan, “Do you want to go first or second?”
Dylan turns to his grandfather for advice. The grandfather knows that Dylan is tired of losing every game to his brother. What does he whisper to Dylan?
And here's the solution:
Dylan should go first. By doing this, Dylan can guarantee a win by playing to a deliberate strategy. On his first turn, he can place a quarter right on the center of the table. Because the table is symmetric, whenever Austin places a quarter on the table, Dylan simply "mirrors" his brother’s placement around the center quarter when it is his turn. For example, if Austin places a quarter near a corner of the table, Dylan can place one on the opposite corner. This strategy ensures that even when Austin finds an open space, so can Dylan. As a result, Dylan gains victory, since Austin will run out of free space first!
This one, from June 2016, requires a bit more math.
Submitted by Robert B., NSA Applied Mathematician
Following their latest trip, the 13 pirates of the ship, SIGINTIA, gather at their favorite tavern to discuss how to divvy up their plunder of gold coins. After much debate, Captain Code Breaker says, “Argggg, it must be evenly distributed amongst all of us. Argggg.” Hence, the captain begins to pass out the coins one by one as each pirate anxiously awaits her reward. However, when the captain gets close to the end of the pile, she realizes there are three extra coins.
After a brief silence, one of the pirates says, “I deserve an extra coin because I loaded the ship while the rest of you slept.” Another pirate states, “Well, I should have an extra coin because I did all the cooking.” Eventually, a brawl ensues over who should get the remaining three coins. The tavern keeper, annoyed by the chaos, kicks out a pirate who has broken a table and who is forced to return her coins. Then the tavern owner yells, “Keep the peace or all of you must go!”
The pirates return to their seats and the captain, left with only 12 total pirates, continues to distribute the coins - “one for you,” “one for you.” Now, as the pile is almost depleted, she realizes that there are five extra coins. Immediately, the pirates again argue over the five extra coins. The captain, fearing that they will be kicked out, grabs the angriest pirate and ushers her out of the tavern with no compensation. With only 11 pirates left, she resumes distribution. As the pile nears depletion, she sees that there won’t be any extra coins. The captain breathes a sigh of relief. No arguments occur and everyone goes to bed in peace.
If there were less than 1,000 coins, how many did the pirates have to divvy up?
See the rest of the story at Business Insider