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Maths Week puzzles: The Answers

Each day this week we’ve been tickling your brains with numerical teasers – here are the answers you’ve been waiting for.

Image: abacus via Shutterstock

EACH DAY THIS week we’ve been entertaining – or torturing – you with a maths teaser.

We haven’t been doing it out of sheer cruelty – all this week, libraries, colleges, universities and other groups have been running events to and the practical benefits of basic numeracy skills to our everyday life.

And here are the answers you’ve been waiting for. Let us know how you did…

Monday’s puzzle: A cash collection was made around a room with everyone putting a note into a bag. People put in either a €20, a €10 or a €5 note.

I asked the collector how much was in the collection and he told me that if I pulled out a note at random that there would be a 1 in 12 chance of getting a €20 note. He said there would be a 1 in 4 chance of getting a €10 note and a 2 in 3 chance of getting a €5.

I protested that I needed more information. He conceded that four people had put in €20 notes and he refused to tell me any more.

Can you figure out how much money was in the bag?

The choices were:

  • €255
  • €360
  • €280
  • €325

Answer: €360

Tuesday’s puzzle: A teacher did a little survey of the pets her pupils had.

Half the children had a dog each and there were three times as many dogs as cats, three more goldfish than cats and two hamsters.

How many pets altogether?

The choices were:

  • 27
  • 52
  • 30
  • 25

Answer: 30 pets altogether – 15 dogs, 5 cats, 8 goldfish, 2 hamsters

Wednesday’s puzzle: You are travelling to Britain and you change €500 into Sterling. The exchange sells you Sterling notes at 0.76 £/€ and takes a £2 commission.

On your trip you spend half your Sterling, and when you return you change it back to euro at 0.79 £/€ and the exchange takes €3 commission.

How much are you left with in Euro?

The choices were:

  • €295.62
  • €240.51
  • €256.08
  • €236.24

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Answer: €236.24

Thursday’s puzzle: I realised that I take around 60 seconds to brush my teeth and I’m in the habit of leaving the tap running. I measured that the tap will fill a 2 litre jug in 16 seconds. I decided to just allow the water to flow while I was rinsing the brush and my mouth. I could accomplish this in 10 seconds.

Assuming that I brush my teeth twice a day at home, how much water will I save in a year?

The choices were:

  • 3,874.75 litres per year
  • 2,757 litres per year
  • 3,230 litres per year
  • 4,562.5 litres per year

Answer: 4,562.5 litres = 4.56 m³

Friday’s puzzle: I found a piece of paper with the following list of numbers on it. The end of the note was torn off. What do you think the next number should be?

Answer: 11

These handy tips will help develop your child’s maths skills (without them knowing it)>

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