#51 Birthday candles
It is Tom’s 7th birthday and he has a cake with seven candles on it, arranged in a circle – but they are trick candles. If you blow on a lit candle, it will go out, but if you blow on an unlit candle, it will relight itself.
Since Tom is only 7, his aim isn’t brilliant. Any time he blows on a particular candle, the two either side also get blown on as well. How can Tom blow out all the candles? What is the fewest number of puffs he can do it in?
Answer next week
#50 Crossing the river
Solution
If Petal places one oar with both ends on the bank, it cuts off a sliver of the bend. Putting the other paddle perpendicular to this will let Petal skedaddle over the paddles and pick up Gretel’s kettle.
You can demonstrate this using Pythagoras’ theorem: B2 = 62 – 1.52 meaning B = √(62 –1.52) = 5.81
So the point where the oars meet is 5.81 metres from the island’s centre, or 2.81m from its edge. We are told the oars are just short of 3m, so they should be long enough – and hopefully strong enough too.
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Quick quiz #43
1 The five most abundant chemical elements in the universe are hydrogen, helium, oxygen, carbon and which other?
2 On which bridge in northern England is the design of Sydney Harbour Bridge based?
3 More than 70 per cent of the world’s pistachios are produced by Iran and which other nation?
4 What day followed Wednesday 2 September 1752 in England and Wales?
5 What does a phlebotomist do?
Answers below
Quick quiz #43
Answers
1 Neon, comprising 0.13 per cent of the universe. Large amounts of it are made in stars through the alpha process of nuclear fusion
2 The Tyne Bridge in Newcastle
3 The US
4 Thursday 14 September 1752, thanks to the switch from the Julian to the Gregorian calendar to catch up with the sun
5 Draws blood for medical purposes