"What is it that never was and never will be."
Li'l Turtle:
"Nothing?"
If it was up to me I would say, ?'congratulations'. However, as the answer is, "a mouse's nest in a cat's ear." I will have to limit myself to, ?'good try'.
Mark:
MESSENGER
1+sqrt(2) km
Here is the simple answer:
The messenger has to have traveled 2 km. It doesn't matter what speed they walked at. At the beginning of the puzzle, the line is 1 km long. The general is therefore 1km ahead of him. He must therefore travel more than 1 km to reach the general. Since the line moves 1000 m, or 1 km forward, the end is where the beginning was. Even if he walked 1.5 km to the general, he only has to walk .5 km to get back to the end of the line. It goes faster going back, because now they are coming towards him, and not going away.
AND NOW FOR THE MORE CALCULATED ANSWER:
Let's denote the speed of the line of soldiers by W and the speed of messenger by V. Let t1 denote the time it takes the messenger to reach captain and t2 the time it takes him to get back to the end of the line.
The troop has travelled 1000m in time (t1+t2), so:
1000m = W (t1+t2)
t1+t2 = 1000m/W
At the same time both in time t1 and t2 the messenger travels 1000m relative to the column, so:
t1 = 1000m/(V-W)
t2 = 1000m/(V+W)
This gives equation:
1000m/W = 1000m/(V-W) + 1000m/(V+W)
When you divide the numenators by 1000m, the denominators by W, and denote V/W by A you obtain:
1 = 1/(A-1) + 1/(A+1)
A^2 - 1 = 2A
Solving that quadratic formula for A you obtain 1+sqrt(2) and 1-sqrt(2). Since V/W can't be negative it turns out V/W = 1+sqrt(2).
The distance travelled by the messenger is:
V (t1+t2) = V ( 1000m/(V-W) + 1000m/(V+W) ) = 1000m ( 1/(1-1/A) + 1/(1+1/A) )
After you plug in A and simplify:
1000m ( 1+sqrt(2) )
and that is approximately 2414,21 m.
A and B is equal to the intersection of C and D.
Mark:
I would guess yes.
Good guess.
Let z=x+i*y. Then A and B are the real and imaginary parts of
z^2=3i+1/z, and C, D are likewise Re and Im of z^3-3iz=1, and
the two equations are plainly equivalent. Alternatively, having
seen this, we can formulate a solution that avoids explicitly
invoking the complex numbers, starting with C=xA-yB, D=yA+xB.
The sequence of digits
1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4 1 5 1 6 1 7 1 8 1 9 2 0 2 1 ...
Is obtained by writing the positive integers in order. If the 10^n th digit in this sequence occurs in the part of the sequence in which the m-digit numbers are placed, define f(n) to be m. For example f(2) = 2 because the 100th digit enters the sequence in the placement of the two-digit integer 55.
Can anyone find, f(1987)
There is an old story of a trader who put into Philadelphia with a boat load of shingles, some which had been damaged in passage. He was asked by a Quaker merchant what the price was for the shingles.
"They are $10 a bundle," he replied, "if you choose the bundles and $5 a bundle if I choose them."
The merchant thought for a minute and said, "... ".
What is the best deal he could make
Here is a riddle, which involves a similar principle:
A man had an apple stand and sold his larger apples at 3 for a dollar and his smaller apples at 5 for a dollar. When he had just 30 apples of each size left to sell, he asked his son to watch the stand while he had lunch.
When he came back from lunch the apples were all gone and the son gave his father $15. The father questioned his son. "You should have received $10 for the large apples and $6 for the 30 small apples, making $16 dollars in all."
The son looked surprised. "I am sure I gave you all the money I received and I counted the change most carefully. It was difficult to manage without you here, and as there were an equal number of each sized apple left, I sold them all at the average price of 4 for $1. Four goes into 60 15 times so I am sure $15 is correct."
Where did the $1 go