I wouldn’t call this a riddle (it’s more like a trick) but some of you may find it as interesting as some of my students did. (This is how I’d bribe them to behave. If, for example, they would go a whole week without anyone making a silly reference to a popular soft drink with the same name, then I’d show them a trick.)
Have someone pick a two digit number and cube it (let’s pick 58; 58 x 58 x 58 = 195,112). Now they tell you what the result is and you calculate the cube root in your head and tell them the original number.
Here’s how to do it:
If the number is in the following range The first digit is
0 to 1,000 0
1,000 to 8,000 1
8,000 to 27,000 2
27,000 to 64,000 3
64,000 to 125,000 4
125,000 to 216,000 5
216,000 to 343,000 6
343,000 to 512,000 7
512,000 to 729,000 8
729,000 to 1,000,000 9
If the number ends in The second digit is
0 0
1 1
2 8
3 7
4 4
5 5
6 6
7 3
8 2
9 9
Getting back to our example- 195,112 is in the range 125,000 to 216,000 => the first digit is 5 and 195,112 ends with a 2 => the second digit is 8 and we get our original number 58.
Disclaimer- I wouldn’t advise performing this trick on a first date, but if you must- be sure to bring a calculator. Most of the girls I dated couldn’t even square a two digit number in their head, let alone cube a number.
You all have a Gut Shabbos now.