Puzzle 13
After a day picking strawberries, I ended up with a full basket, which is always nice.
I ate 5, and then gave Alex half of the remaining.
I ate another 3, and then gave Billie one third of the remaining.
I ate another 6, and then gave Charlie two thirds of the remaining.
I now had 34 strawberries left. How many did I start with?
Puzzle Copyright © Kevin Stone
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Hint
Try working backwards.
Answer
335 strawberries.
Reasoning
Working backwards...
I ended up with 34 strawberries, so I had 102 before giving Charlie two thirds.
I ate 6 myself, so I had 108 before I ate those.
I had 108 strawberries, so I had 162 before giving Billie one third.
I ate 3 myself, so I had 165 before I ate those.
I had 165 strawberries, so I had 330 before giving Alex one half.
Ate 5 myself, so I had 335 before I ate those.
Therefore, I started with 335 strawberries.
Double-Checking
I started with 335.
I ate 5, leaving 330.
I gave Alex half (165), leaving 165.
I ate 3, leaving 162.
I gave Billie one third (54), leaving 108.
I ate 6, leaving 102.
I gave Charlie two thirds (68), leaving 34.
Puzzle 14
What comes next in this sequence:
elgnairt erauqs nogatnep nogaxeh nogatpeh {?}
Puzzle Copyright © Kevin Stone
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Answer
nogatco.
Reasoning
These are geometric shapes, the number of sides increases, and the words are reversed.
3 elgnairt = triangle
4 erauqs = square
5 nogatnep = pentagon
6 nogaxeh = hexagon
7 nogatpeh = heptagon
8 nogatco = octagon
Puzzle 15
You have a very large number of generic plastic building blocks, each in the shape of a cube.
Think about how many cubes you would need in order to construct a giant cube with 16 small cubes along each edge.
If you were to then remove the outside layer, how many small cubes would you have removed?
Puzzle Copyright © Kevin Stone
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Hint
How large would the smaller cube be?
Answer
1,352 small cubes.
Reasoning
The original large cube with 16 small cubes along each edge would require 16 x 16 x 16 = 4,096 small cubes.
Removing the outside layer would leave a large cube now with 14 small cubes along each edge (which requires 14 x 14 x 14 = 2,744 small cubes).
It isn't 15 small cubes because you're removing both ends of an edge.
Therefore, you have removed 4,096 – 2,744 = 1,352 small cubes.
Puzzle 16
How many squares of any size on this chessboard do not contain a rook?
Puzzle Copyright © Kevin Stone
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Hint
There are no larger squares than size 4x4.
Answer
There are 110 squares without a rook.
Reasoning
There are 60 squares of size 1x1.
There are 35 squares of size 2x2.
There are 12 squares of size 3x3.
There are 3 squares of size 4x4.
Giving a total of 60 + 35 + 12 + 3 = 110 squares.
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