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Original poster

Why is my answer not correct?

61 replies

Ruprekt · 30/10/2013 10:02

24 pirates.

1/3 found gold

1/4 found rubies

1/2 found neither

How many found gold and rubies?

My calc was 8 found gold, 6 found rubies, 12 found nothing.

So, 14 found gold and rubies.....but 14 + 12 = 26........

Waaah

I love literacy but maths aint my thing.......ConfusedConfusedConfused

Please help......

OP posts:
FurryDogMother · 30/10/2013 10:19

Of the 24, 1/2 found nothing, so you're looking at a 'pool' of 12 who found something. Of those, 8 found gold, and 6 found rubies. This means that 6 of the 12 didn't find rubies, but must have found gold (else they'd be in the 12 who found nothing). As 8 found gold, 2 of those must have found rubies too - so my answer would be 2 :)

I could be wrong, of course!

LeMousquetaireAnonyme · 30/10/2013 10:19

8 found gold, 6 found rubies 12 found nothing, so 12 found something...

4 found only rubies, 6 only gold, 2 both answer is 2 found gold AND rubies

It might be all about fractions though for your son homework

TravelinColour · 30/10/2013 10:20

This reply has been deleted

Message withdrawn at poster's request.

BoreOfWhabylon · 30/10/2013 10:20

Surely it must be 2 who found both gold AND rubies?

Half (12) didn't find either

So the other 12 found one or the other or both.

BUT 8 + 6 = 14, not 12

So 2 must have found both. I think Confused

Sparklebum · 30/10/2013 10:20

I would say 2 found gold and.rubies

1/3 gold = 8
1/4 rubies = 6

so 2 found both rubies and gold???

FunkyFucker · 30/10/2013 10:21

1/3 plus 1/4 plus 1/2 = more than 1... so add those together and the proportion over 1 found both.

BoreOfWhabylon · 30/10/2013 10:21

cross posted with everyone else Grin

Sparklebum · 30/10/2013 10:21

Gah took me far to long to.type.thatSmile

Original poster
Ruprekt · 30/10/2013 10:22

Badly written question methinks! Grin

Thanks everyone.

OP posts:
Madamecastafiore · 30/10/2013 10:25

12 found nothing
6 found rubies
8 found gold

So 2 found both.

Failed maths gcse and had to do retake though!

larrygrylls · 30/10/2013 10:28

It is that old topic: Venn diagrams.

12 found nothing, 8 found gold and 6 found rubies.

So draw two intersecting circles. The total number in the Ruby circle is 6, the total number in the gold circle is 8. The only way you can get to 12 finding something is 2 in the intersect, 6 in gold only and 4 in rubies only. The intersect represents finding both.

Someone above showed how to do it with equations, but Venn diagrams are nice and quick.

Try it!

SoupDragon · 30/10/2013 10:35

I suppose the question should be worded "How many found both gold and rubies"

BerstieSpotts · 30/10/2013 10:37

I read the question as how many found both, but I think Soup is right, to eliminate confusion it should have been worded like that.

BerstieSpotts · 30/10/2013 10:38

I would find it very hard to calculate or visualise using venn diagrams. I think I'd have worked it out using the counting method above where it adds up to 26 meaning 2 must have been in two categories.

larrygrylls · 30/10/2013 10:39

Umm, if the answer was 14, the question would have been worded "gold OR rubies". The word "and" implies both.

larrygrylls · 30/10/2013 10:42

"I would find it very hard to calculate or visualise using venn diagrams."

I guess everyone finds different methods easier. However, I suggest that if you lay two big loops (hula hoops or something) on the floor with an overlapping area and you get two different kinds of objects, after a while they become pretty intuitive and easy.

Viviennemary · 30/10/2013 10:42

I'll have a go. 12 didn't find anything. So that leaves 12

8 found gold
6 found rubies

So 14 found something. So how if 12 found nothing. Maths was never my strong point. Grin

throckenholt · 30/10/2013 10:47

it's a logic question.

12 found nothing - leaving 12 others.

8 of those found gold - leaving 4 others. Those 4 others are included in the 6 who found rubies - so 2 must have found both gold and rubies.

OR

6 of those found rubies - leaving 6 others. Those 6 others are included in the 8 who found gold - so 2 must have found both gold and rubies.

Whichever way you do it - you come up with 2 who found both.

larrygrylls · 30/10/2013 11:03

It is set theory, albeit v simple set theory.

BerstieSpotts · 30/10/2013 22:12

I do know how venn diagrams work. It's just using them for this seems backwards to me. If there are 8 in the "gold" circle and 6 in the "rubies" circle, that tells you nothing about how many are in the overlapping circle.

larrygrylls · 31/10/2013 07:34

Bertie,

If you know the total of rubies only, gold only and rubies and gold is 12, and you know the individual totals. You know that x + middle=6, y + middle=8 and x+y+ middle= 12. That is 3 equations in 3 variables, with the only solution of middle=2. A Venn diagram is a visual representation that most people find easier than solving the equations analytically. This is a fact as children are (or at least were) able to access the set solution long before they could solve 3 simultaneous equations in 3 variables.

Imagine if I introduced a 3rd category (sapphires, for instance) and gave enough info to solve, so 7 equations in 7 variables. 3 overlapping circles is just a v easy visualisation.

BerstieSpotts · 31/10/2013 07:42

Yes, ok. I see your point. If you know the total then you can try overlapping them by different amounts and counting to reach the total.

Still it seems long winded Grin But then most things which are supposedly "easier" I seem to find more confusing, I think my brain is just wired to do it in a different way.

larrygrylls · 31/10/2013 08:33

To be honest, I personally prefer lots of equations to pictures. However I have come to realise that I am in a tiny minority. Maybe you are in the same minority! The vast majority of people are visual, though.

Also, set theory does eventually become v analytical and symbolic ( most of which I have forgotten). Venn diagrams are the access point to this branch of maths.

Ihatespiders · 31/10/2013 09:11

With some clearer wording, this is a great puzzle and I shall pinch it for my class!

Makes a change from my usual variations on teachers sharing Quality Street and dropping unsubtle hints that I always eat the purple ones Wink.

SoupDragon · 31/10/2013 09:30

Umm, if the answer was 14, the question would have been worded "gold OR rubies". The word "and" implies both

I agree, but the fact that some people misunderstood the wording shows that it wasn't phrased clearly and that is easily rectified.