Polar bear puzzle

Puzzle:

There is a house with four walls. Each wall faces south. There is a window in each wall.

A bear walks by one of the windows. What colour is the bear?

Solution:
White. If all the walls face south, the house is at the north pole, and the bear, therefore, is a polar bear.

Solution of Bridge crossing Riddle

Solution:
-> 1. + 2. - 2 min
<- 1. - 1 min
-> 3. + 4. - 9 min
<- 2. - 2 min
-> 1. + 2. - 2 min

Total - 16 min
note:
-> forward direction
<- Reverse direction

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Bridge crossing Riddle

Question:
There are four people at the end of bridge. They take following time to cross the bridge:
1st: 1 min
2nd: 2 min
3rd: 7 min
4th: 9 min

Condition: 
1. They have only one torch and they can't cross bridge without torch.
2. and only 2 person can cross bridge at a time.

Solution of Burn the rope....good puzzle

Solution:
Take 2 ropes R1, R2. Light R1 at both ends and R2 at one end. When R1 is completely burned (30 minutes have passed), light R2 at the other end. When R2 is completely burned 45 minutes have passed.

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Burn the rope....good puzzle

Question:
there are unlimited ropes of same length and if we burn them it will take 1 hour.
How to measure 45 mins?