### Rule of Three

If it takes four men one day to build a wall, how long does it take 60,000 men to build a similar wall?

### Crossing the Atlantic

Every day at noon a boat leaves Le Havre for New York while another boat leaves New York for Le Havre. The ocean crossing takes seven days. How many boats will each boat cross during their journey?

### On Time

On a clock the three hands - the second, minute and hour hands - are on the same axis. How often in a 24 hour day will the second hand be parallel to either of the two other hands?

# Christmas Trees

##### Stage: 3 Challenge Level:

The following solution is from Xinxin, Tao Nan School, Singapore

Of the 12 shortest trees, A is the tallest. Nevertheless it is the shortest in its column.

Of the 10 tallest trees, B is the shortest. Nevertheless it is the tallest in its row.

The row where B is and the column where A is intersect at a tree. Let us call this tree C.

Now, C is definitely shorter than B because B is the tallest in C's row. In terms of height, C < B

And of course, A is definitely shorter than C because A is the shortest in C's column.
In terms of height, A < C

If A < C and C < B then A < C

Thus A < B

So B is taller than A.