MATH MONDAY - Easy as 1-2-3 (4-5-6-7-8-9)
Okay, yes, we hear you - the locker puzzle was really hard. This week’s Math Monday is a little less diabolical (but it’s not, like, easy or anything…where would the fun be in that?).
Today’s Puzzle
How can you make 100 by interspersing any number of pluses and minuses into the string of digits 9 8 7 6 5 4 3 2 1? (You can’t change the order of the digits.)
There is more than one correct answer here - for a challenge, try to find the answer with the fewest pluses and minuses.
Saturday’s Puzzle - 🤖💰🔥
You find yourself in a room with two doors guarded by two robots. One door leads to a mountain of treasure, while the other leads to a lake of molten lava. One robot always tells the truth and the other always lies. You can ask only one question. What do you ask to figure out which door leads to the treasure?
[SPOILER] Answer to Saturday’s Puzzle
Ask one of the robots, “What would the other robot say if I asked which door leads to the treasure?”
Then do the opposite.
Explanation: If you ask the honest robot, it will tell you that the lying robot would point to the door leading to the lava lake. If you ask the lying robot, it will lie and tell you that the honest robot would point to the lava door too. Since you know that both robots will point to the lava door, you simply go through the other one and claim your treasure!
This is a variation of a famous “knights and knaves” problem (see the “Fork in the road” section here), which refers to any type of puzzle involving always-lying or always-honest characters. In this one, the key idea is to figure out a question where both robots will say the same thing about each door. That way, no matter which one you’re talking to, you know which door to choose.