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Maths question

10 replies

JustCallMeJones · 30/04/2018 18:48

I’m rubbish and hope you can help.

Out of the 240 children in ks2, 3:8 children have blue eyes. This is half of the proportion of the KS1 children. If there are 180 children in KS1, how many KS1 children have blue eyes?

120. 190. Or. 135

What is the ratio
What is the proportion

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MangoBiscuit · 30/04/2018 19:01

I'm not sure the notation is correct. I thought 3:8 meant 3 to 8, not 3 in 8, but otherwise the options don't work.

Double 3 in 8 gives 6 in 8, or 75%. 75% of 180 is 135.

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xyzandabc · 30/04/2018 19:01

It's a badly worded question. Not particularly clear at all.

If 3/8 is half the proportion of the KS1 with blue eyes, then the proportion of KS1 with blue eyes is 6/8.

6/8 of 180 is 135. So 135 have blue eyes in KS1

The ratio of what?
90 KS2 have blue eyes, 135 KS1 have blue eyes so the ration would be 90:135
This can be reduced to 2:3. So for every 2 KS2 blue eyed kids, there will be 3 KS1 blue eyed kids.

The proportion of what?
Proportion of KS1 with blue eyes is 6/8 = 3/4 = 75%
Proportion overall would be (90+135)/(240+180) = 125/420 = 29.7%

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xyzandabc · 30/04/2018 19:04

Mango is right, I think my way is what they are looking for, but it should have been written 3/8 not 3:8.
I stand by my 1st sentence, it's not a well written question!

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JustCallMeJones · 30/04/2018 19:09

Thank you, no wonder Ds and I are confused

I’ll have a good read through your answers in a wee while.

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JustCallMeJones · 30/04/2018 19:12

They are currently going over ratios

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TheThickenPlots · 30/04/2018 19:25

As a secondary maths teacher I’d say that question was rubbish! 3:8 would be 3/11 of the Children in ks2 had blue eyes and therefore 6/11 in ks1- which doesn’t fit any of the answers. They must mean 3/8 which would mean 6/8 of ks1 had blue eyes (135). Primary schools are often rubbish at ratio, students get some weird ideas and always try and use it for probability (incorrectly!)

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Lougle · 30/04/2018 19:32

I think they mean ⅜ of KS2 children have blue eyes which is 240÷8= 30; 30×3= 90 children.

They then want you to realise that 6/8 can reduce to ¾ and they are writing it (wrongly) 3:4, so 180÷4= 45; 45×3= 135 children.

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FiveMoreMinutesPlease · 30/04/2018 19:39

6:8
135

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Tomorrowillbeachicken · 30/04/2018 19:55

I’d say 135 as it’s 3/4

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JustCallMeJones · 30/04/2018 20:34

Thanks for clarifying. I was trying my hardest to understand but it didn’t make sense.