You are decorating for spring and you’ve found a bargain. A huge box of beautifully decorated tiles, enough to provide a border in two rooms. You really can’t figure out how to arrange them. If you set a border of two tiles all around, there’s one left over. If you set three tiles all around or four or five or six there’s still one tile left over. Finally you try a block of seven tiles for each corner and you come out even. What is the smallest number of tiles you could have to get this result?
A pencil. It’s wooden, is covered in paint and the output of a pencil in the form of writing or art can make you laugh or cry. And graphite is the dark part inside.
I see much but change little,
I am firm, irresolute,
Powerful but gentle,
I can rip apart mountains,
Yet be moved by gentle stirrings,
I am valued and wasted,
I am life itself,
And I give life to others.
A tree. A tall one can see long distances but don’t change much. They are strong and powerful, and the roots of a tree can slowly tear apart a mountain. The gentle stirrings of the wind can blow their branches and leaves. Trees are valuable as they provide wood and paper, but they are also wasted. And lastly, trees, like all plants, provide us with life-giving oxygen.
A princess is as old as the prince will be when the princess is twice the age that the prince was when the princess’s age was half the sum of their present ages.
This one took a while to figure out and there are numerous valid ways of finding the answer.
Here is the solution I came up with
I created the following table from the riddle:
Current
Future
Past
Princess
x
2z
(x+y)/2
Prince
y
x
z
I then created three equations, since the difference in their age will always be the same.
d = the difference in ages
x – y = d
2z – x = d
x/2 + y/2 – z = d
I then created a matrix and solved it using row reduction.
x
y
z
1
-1
0
d
-1
0
2
d
.5
.5
-1
d
It reduced to:
x
y
z
1
0
0
4d
0
1
0
3d
0
0
1
5d/2
This means that you can pick any difference you want (an even one presumably because you want integer ages).
Princess age: 4d
Prince age: 3d
Ages that work
Princess
Prince
4
3
8
6
16
12
24
18
32
24
40
30
48
36
56
42
64
48
72
54
80
60
To see other solutions check out the comments from when I posted this on my blog.
