"At night they come without being fetched,
And by day they are lost without being stolen."

Today, John has to transfer 50 euro to the bank account of a Dutch friend. He has written down the account number on a piece paper. But since he had forgotten to take out the paper from his trousers when he put them in the washing machine, one digit of the bank account number became unreadable. The note says: 3170?4847. The friend of John is climbing the Mount Everest at the moment, so it is impossible for John to call his friend. Suddenly he remembers that a for a valid Dutch bank account number it holds that the first digit times 9 + the second digit times 8 + the third digit times 7 + ...... + the nineth digit times 1 should be divisible by 11. John thinks for a moment and finds the correct number. What is it?

A wire with a length of 60 meter is hanging between two high voltage pylons. The wire is connected to the pylons at a height of 50 meters. The middle part of the wire is 20 meters above ground level. How far are the high voltage pylons standing apart?