#14 The H coins problem
Seven coins have been placed in the 鈥淗鈥� shape above. Altogether there are five lines of three, including the diagonals.
Your challenge is to place two more coins so that you can make 10 straight lines of three. No stacking of coins or other sneaky trick is required.
If you find a way to do this, give yourself a silver medal. If you find a second way to do it that isn鈥檛 a mirror image of the first, award yourself a gold.
Answer next week
#13 Snail party
Solution
As the four snails move towards each other they point at all times at the snail they are moving towards. They thus keep to the corners of a rotating, ever decreasing square.
As A, for example, changes direction, so do B, C and D, all by the same amount, so their paths are constantly at right angles. This means that A, for example, always comes towards B at the same constant speed it did at the start, continuing until they meet.
This is exactly the same situation as if B were stationary and A moved directly towards it. Thus the time taken is the initial distance, 2 metres, divided by the speed, 2 metres per hour, which equals 1 hour.
Quick Quiz #13
1 What speed is required to go hypersonic?
2 Plants of the genus Nepenthes are most notorious for what?
3 Dotted with more than 400 volcanoes, what is the most tectonically active body in the solar system?
4 The abandoned whaling station Grytviken is the only settlement on which UK island territory in the South Atlantic, also home to the grave of polar explorer Ernest Shackleton?
5 Where are the Islets of Langerhans?
Answers below
Quick Quiz #13
Answers
1 Mach 5, five times the speed of sound
2 Eating insects. They are carnivorous tropical pitcher plants
3 Jupiter鈥檚 moon Io
4 South Georgia
5 The pancreas. They contain its insulin-producing cells and are named for their discoverer, the German anatomist Paul Langerhans
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