Easy:
A rope ladder hangs over the side of a ship so that the ladder just reaches the water. The rungs are 25 cm apart. How many rungs will be under water when the tide has risen one metre?
Hard:
A high school has a strange principal. On the first day, he has his students perform an odd opening day ceremony:
There
are one thousand lockers and one thousand students in the school. The
principal asks the first student to go to every locker and open it. Then
he has the second student go to every second locker and close it. The
third goes to every third locker and, if it is closed, he opens it, and
if it is open, he closes it. The fourth student does this to every
fourth locker, and so on. After the process is completed with the
thousandth student, how many lockers are open?
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