Choose any convex polyhedron you like. Count its total faces and vertices, add them together, and then subtract its total number of edges. What invariant integer will your calculation always yield?
2
According to Euler's polyhedron formula, V - E + F = 2 for any convex three-dimensional polyhedron.
About this riddle
Math riddles hide a calculation inside a short story. Pull out the numbers, work out what is being asked, and watch for a trick such as a unit change.
Difficulty: Easy. More like this: Math riddles with answers or try Target 24 for a different kind of puzzle.
More math riddles
If it takes 5 identical industrial machines 5 minutes to manufacture 5 customized bolts, how many minutes will it take 100 of those same machines to manufacture 100 customized bolts?
A rectangle has an area of 48 square centimeters. Its length is 3 times its width. What is the perimeter of the rectangle in centimeters?
I am a two-digit prime number less than 30. Dividing me by 4 leaves a remainder of 3. Adding 2 to me turns me into a multiple of 5. What number am I?
I have four legs inside my house when I am alone, but when my dog joins me, we have ten legs altogether. How many legs do I have?
What is the next number in this geometric sequence: 3, 6, 12, 24, ...?
We are two consecutive prime numbers. Multiply us together and you get 323. Add us together and you get 36. What two numbers are we?