Four Digit Number

The first digit is one third of the second digit

The third digit is the sum of the first two digits

The fourth digit is three times the second digit

What is the number?


Two trains run between stations at A and B

The first train runs from A to B  at 85mph

The second train runs from B to A at 105mph

How far apart will the trains be 30 minutes before they pass each other?

12 Marbles

You have 12 marbles

The marbles are all the same size, shape and colour – they look identical

One marble is heavier in weight than the others

How can you work out which marble is the heavier one, using only a balance scale, if you can only use the balance scale 3 times to work out the answer?