My wife recently purchased a Mensa book from a charity shop (thrift shop) which was published by British Mensa Limited in 1996. The book is called MENSA presents Logic puzzles.
I would like peoples opinions on this question and answer:
Question.
Carrier Pigeons
A driver approaches a bridge. He notices that the maximum weight allowed is 20 tons and knows that his empty pantechnicon (removal van ) weighs 20 tons. However, he has a cargo of 200 pigeons which weigh 1lb each. As the pigeons are asleep on perches he stops the vehicle, bangs on the side to waken the birds who start flying around, then safely drives over the bridge.
Is he correct?
Answer.
No. The pigeons remain at 200lbs even whilst flying. Those flying up would reduce the weight, but those flying down would increase the weight, so balancing the total weight.
end of answer.
I don't understand this answer. For example, if it was a very tall vehicle and all the pigeons were flying upwards at the same time then does that mean the van weighs less than if they were all flying down at the same time? Surely the answer should have been Yes, the driver is correct. Or am I missing something?