One year in the nineteenth century, the mathematician De Morgan remarked, 'my age now is the square root of this year'. When was De Morgan born?

2.5 bottles of the same size are filled with 1.5 litres of water. How many millilitres does each bottle contain?

What is the remainder on dividing the sum 2 + 2 squared + 2 cubed + ... + 2 to the power 10 by 10?

The empty squares below are to be filled by writing numbers: 1, blank, blank, blank, blank, 6 (six squares in a row). The sum of the numbers in any three consecutive squares must be 10. What number should be written on the second square?

Between 1 and 100, how many numbers are there with exactly three factors?