#32 Rearranging books
Once a week, it is Jordie鈥檚 job at the library to put books back in order on the shelves.
This week, he finds that the 10-volume encyclopedia has been mixed up in the order shown above. He has to put them back in order, and since the books are heavy, he wants to move as few volumes as possible.
A move consists of taking a book off the shelf and sliding the other books to the side to make space, if necessary. What is the smallest number of moves he needs to make to rearrange the books in the order one to 10 from left to right?
Answer next week
#31 Three hats
Solution
Cassie can鈥檛 deduce the colour of her hat from looking at the two in front of her, so she says nothing. This silence tells Ariana and Beverley that their hats are different colours. Beverley can see a white hat in front of her, so she says 鈥渂lack鈥�. Ariana then deduces that her hat is white.
Quick quiz #30
1 Panthera pardus pardus, Loxodonta africana, Diceros bicornis, Syncerus caffer鈥� what is missing from the list?
2 When viewed from the northern hemisphere, does the moon appear to be the same way up as it looks from the southern hemisphere or is it upside down?
3 Russia鈥檚 Lake Baikal is the world鈥檚 deepest lake and its largest freshwater lake by volume. Which lake is second on both of these lists?
4 What creature, when discovered swimming off the eastern coast of South Africa in 1938, had been missing for some 66 million years?
5 The five telescopes of the High Energy Spectroscopic System in Namibia investigate which phenomenon?
Answers below
Quick Quiz #30
Answers
1 Panthera leo, the lion. Together with the African leopard, the African bush elephant, the black rhinoceros and the Cape buffalo, it makes up the 鈥淏ig Five鈥� of African game
2 Upside down
3 Lake Tanganyika in East Africa鈥檚 Great Rift Valley
4 The coelacanth. The fish, previously known only from fossils, was thought to have become extinct around the time the dinosaurs did
5 Cosmic rays, specifically gamma rays