I'VE finally had a chance to catch up with all the brain teasers you've sent in recently, and the biggest puzzle for me is how to fit your correspondence into one small column.

Don Hinson of Chesham brought lots of response with two teasers.

The first went: "There are nine cows in a field, and a farmer wants to build four fenced-in enclosures so that each contains an odd number of cows. How can he do this?"

Best answer came from Maurice Allen of Little Marlow who replied: "You put up three enclosed pens each with three cows in, then build a larger pen around outside which will include the nine cows."

I had various other good, but more complicated answers. Reader V Searle of Cressex got around the lack of odd numbers by suggesting that one of the cows was pregnant, resulting in there being ten cows.

Don's second puzzle read: "Water lilies are growing on a pond. The area they cover doubles in 24 hours. The pond becomes full on the 12th day. On which day was the pond half full?"

The answer was the 11th day. L Rashbrook of High Wycombe had one of the most concise answers: "As the water lilies double in area each 24 hours, the pond must have been half full on the 11th day."

Meanwhile, Maurice Allen had also sent in his own puzzle a few weeks ago: "It read: "A hill is two miles long, one mile up and one mile down. A car goes up one side at 30 miles per hour. At what speed would it have to descend to make an average speed of 60 miles per hour for the complete hill?"

Several readers said 90mph. Maurice didn't give an answer, but I'm inclined to go with the one suggested by Brian Morgan of Holmer Green. He writes: "The car takes as long to ascend the first half of the journey as it is allowed to complete the whole of the journey. Hence the speed required for the second half is infinity."

In other words, it's impossible.

I've had a mountain of other post, but strangely no answer appears to be forthcoming to Mrs Searle's teaser of December 7 about a laundry. If anyone still remembers, the answer was that it was a trick question relying on the fact 11.30 was at night and not in the morning.

Still, I'm shocked there was no response, because I had offered a free flap jack from Karen the Star sandwich lady to the first person with the correct answer.

The flap jack is now sitting sadly by the side of my desk. So I'll give it to the reader who sends in the first correct answer to a puzzle from Brian Morgan.

He simply asks: "What does N stand for?"