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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 highlightmathsweek.ie 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:
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:
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:
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:
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
Friday’s answer = 11
Why?
The written numbers are the number of digital lines making up the preceding number.
It was too simple! Pointless really…
I got it by chance. I saw the difference between the pairs of digital numbers was 6, 6, 12, 12. I thought then the penned in numbers had a similar pattern 7, 9, 9, 11. I thought there must be another 11 then. The real reason makes more sense but it’s funny how this worked out.
Maybe yours is the real reason and mine is by chance.
We’ll probably never know.
Did the same as Mr Dragmire.
You still recognised the pattern Mr dragmire.
Geez, no explanation for Friday’s answer which wasn’t a maths puzzle and no clarification for Tuesday’s mess up either, ending with a whimper.
Tuesday’s was OK – the absence of explanation was unfortunate.
Half the children had a dog – so their can’t be 25 or 27 children, other wise you have half a dog!
So there were either 15 or 26 Dogs
But there were 3 times as many dogs as cats – so which of 15 & 26 is divisible by 3?
OK
15 dogs, 5 cats, 8 goldfish & 2 hamsters – 30 pets – and also 30 children.
It wanted number of pets not number of students. 24 students would have 25 pets between them and 30 students would have 30 pets between them. The only conditions are that total #students must be divisible by 6 and that total #pets must be divisible by 5.
Tuesdays answer could have been 25 also. 12 dogs, 4 cats, 7 goldfish & 2 hamsters equal 25.
All the people that got their knickers in a twist on Tuesday can now un twist them :)
But they haven’t cleared up the confusion despite the reams of comments pointing out their mistake.
What was their mistake on Tuesday? I can’t see one.
With the way the question was phrased both 25 and 30 are possible answers.
The answer is dependant on the assumption that each child only has one pet. It may seem trivial but saying that half the children have dogs doesn’t help at all without that knowledge. It should have just said half the pets are dogs or made it clear that each child had only one pet.
Ok – I see how that could be possible if you allow for a pupil having two pets.
A bit of a contrived gripe in my view.
Not really contrived in my opinion. That caught me up as well until I said fe<k it and just made the assumption. I wrote it in my copy book and everything. Really should have stated it in the question.
Has Jane found out how many kids were in that classroom ? Classic!!
Have you figured out that 72 isn’t the answer to today’s one?
Yes I have ,Leopold.
4/5 not bad, water one got me.
water a vexed question right now – especially if one is asked to pay for it.
Professor layton; journal style
I thought the teeth brushing one was poorly worded. I got the “correct” answer if I based the time on 50 mins ie subtracting the rinsing time.
Seconds not mins!
72 should have been the right answer ..
72 is the right answer if you’re looking at the big numbers.
But the next number will be one of the faint numbers.
I think it’s 11.
If you loop the faint numbers, skipping one number each time, you get 11.
The 7 goes with the second 9
And the first 9 goes with the first 11
So the next loop would make it 7 to 9 to 11. The loops are overlapping
a
have your say