1)   NORTH POLE ….
If you start from the north pole to  1 mile  south and 1 mile west and 1 mile north ..you’ll  follow a triangular path and end up on the same spot. (remember its a sphere not a rectangle visualize it )

2) SOUTH POLE…

At a particular distance from the south pole ..if you consider a circle of circumference = 1 miles then  (AS SHOWN IN THE FIGURE ABOVE)
when you start 1 miles  above  that circle  and follow the direction ( 1 south 1 west 1 north) you’ll end up in the same spot.
NOTE : When you travel south you’ll end up in the circumference of the circle
when you go towards west  you will  travel around the complete circle once(circumference = 1 miles) and end up at the point on the circle where you started
then travel back to north to end up in the same spot..
So in this case you can start at any point above 1 miles  of  this circle….so the possible solution is INFINITE.

44 METERS.

we konw ,
speed = distance/time        & length of bridge = 2x

If john runs back , he misses the train by just 4 meters that means ,
that means (time taken by john to reach the right end of bridge) = (time taken by the train to reach 4meters before the start of bridge)
speed (train) = 90kmph = (2x – 4)/t         &          speed (john) = (x-10)/t      {refer the above diagram}
                  t = (2x-4)/90 = (x-10)/speed(john)   ………………………………(1)

similarly,
if john runs to the left of the bridge the train hits him 8 meters before the end so,
   (time taken by the train  to reach 8 meters before left end of the bridge ) = time taken by john to reach 8 meters before the left end of the bridge)
speed(train) = 90 = (2x + 2x -8)/t*          &     speed(john) = (x -8 + 10) / t*

              t* = (4x-8)/90 = (x+2)/speed(john) 
   so,
              speed(john) = (x+2)/(4x-8)(90) ……………………………………………(2)

substitute(2) in equation (1)…..
                                     you get the answer.
NOTE: (The units does not matter as it is going to get cancelled from both RHS and LHS)

94 CHICKNS + 5 hORSES + 1 PIG
94  chickens = 94 * 50 cents = 4700 cents = 47 euros.
5 horses = 5 * 10 = 50 euros
1 pig = 3 euros.

First of all..
Let us assume that all 10 bags contain marbles weighing 10gms each..
so if you take 1 marble from the first bag
2 marbles from the second bag
3 marbles from the third bag
.
.
.
10 marbles from the tenth bag
The total weight when measured will be (10+20+30+40+…..100)=  550gms
BUT ,
      one of the bag contains marbles which are 9gms each……
so  in case if it was from the first bag ,when you  weigh  = ( 9+20+30+….100)=549gms
if it was from the second bag,                                      (10+18+30+40+….100)=548gms
if it was from the third bag,                                          (10+20+27+40+…..100)=547gms
.
.
.
similarly you can find which is the defective one by weighing only once.