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 Post subject: Re: Simultaneous Equations QuestionsPosted: Tue May 22, 2018 10:56 am

Joined: Fri Mar 10, 2017 5:06 pm
Posts: 682
Guest55 wrote:
Surferfish wrote:
But that is exactly the same as the way I did it.

The "algebra" is just a neat, shorthand way of writing down the thought process which you went through and described in English words.

With respect, it is not - you introduced notation which was unnecessary and I'd mark it wrong as you did not define your variables.

So how would you solve and explain the answer to the question asked by the OP then? (the one about teas and coffees rather than ice creams)

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 Post subject: Re: Simultaneous Equations QuestionsPosted: Tue May 22, 2018 11:24 am

Joined: Sat Oct 08, 2011 2:25 pm
Posts: 2246
For me I'd just say 4 teas and coffees were £12 so add 25% to get a price for 5.

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 Post subject: Re: Simultaneous Equations QuestionsPosted: Tue May 22, 2018 2:47 pm

Joined: Mon Feb 12, 2007 2:21 pm
Posts: 16254
Question: Andrew paid £12 for 4 cups of coffee and 4 cups of tea.
3 cups of coffee cost as much as 2 cups of tea.
What was the total cost of 5 cups of tea and 5 cups of coffee?

I'd say one cup of coffee and one cup of tea must be £3. So 5 of each is £15.

If you want to use letters you need to say what they represent e.g. let c be the cost in £ of a cup of coffee and t be the cost in £ of a cup of tea.

The example I wrote is a more usual format of this type.

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 Post subject: Re: Simultaneous Equations QuestionsPosted: Tue May 22, 2018 2:49 pm

Joined: Sat Oct 08, 2011 2:25 pm
Posts: 2246
Good to see G55 back-pedalling a bit...

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 Post subject: Re: Simultaneous Equations QuestionsPosted: Tue May 22, 2018 3:00 pm

Joined: Mon Feb 12, 2007 2:21 pm
Posts: 16254
Where am I back-pedalling? Any student that used algebra would be marked down - it's a complete waste of time. Look at all that writing just to define the variables and then you have to form the equations ...

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 Post subject: Re: Simultaneous Equations QuestionsPosted: Tue May 22, 2018 3:36 pm

Joined: Sat Oct 08, 2011 2:25 pm
Posts: 2246
Guest55 wrote:
Where am I back-pedalling? Any student that used algebra would be marked down - it's a complete waste of time. Look at all that writing just to define the variables and then you have to form the equations ...

Can you even be marked down for using a correct mathematical process, albeit long winded, and getting the correct answer? (Unless of course it asks for a specific way)

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 Post subject: Re: Simultaneous Equations QuestionsPosted: Tue May 22, 2018 3:40 pm

Joined: Mon Feb 12, 2007 2:21 pm
Posts: 16254
You can in some circumstances in GCSE [e.g. if you use a method it tells you not to]- in Year 7 we try to encourage appropriate methods so some of our mark scheme 'reward' efficient approaches. You don't have time in GCSE and A level to use long-winded approaches ...

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 Post subject: Re: Simultaneous Equations QuestionsPosted: Tue May 22, 2018 3:49 pm

Joined: Fri Mar 10, 2017 5:06 pm
Posts: 682
It is far quicker to write

'c + t = 3' (5 characters)

than it is to write

'one cup of coffee and one cup of tea must be £3' (36 characters)

over 7 times as quick in fact!

I agree that in a proper mathematical proof you should define each variable, but in a simple example like this it should be quite obvious what 'c' and 't' stand for and seems a bit harsh to mark someone wrong for neglecting to formally define them.

If you want to be so strict about it I could just as well ask why 'one cup of coffee and one cup of tea must be £3' as you just stated. You've made a bit of a logical jump there haven't you in assuming that we all understand that its because £12 divided by 4 equals £3? Is that any different in me assuming that everyone understands what 'c' and 't' stand for in my shorthand notation?

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 Post subject: Re: Simultaneous Equations QuestionsPosted: Tue May 22, 2018 3:50 pm

Joined: Sat Oct 08, 2011 2:25 pm
Posts: 2246
Guest55 wrote:
You can in some circumstances in GCSE [e.g. if you use a method it tells you not to]- in Year 7 we try to encourage appropriate methods so some of our mark scheme 'reward' efficient approaches. You don't have time in GCSE and A level to use long-winded approaches ...

I agree with you totally but I would also say that if that is how a student can best solve the problem and will be able to use post school, stuff the gcse mark..

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 Post subject: Re: Simultaneous Equations QuestionsPosted: Tue May 22, 2018 3:53 pm

Joined: Mon Feb 12, 2007 2:21 pm
Posts: 16254
You must define variables or it is wrong. in this case, c could be the number of cups or the cost or ....

In an exam I would have written '1 cup coffee and 1 cup tea costs 12/4 = £3'

Look, algebra is not needed here - it's not taught at Primary so it is inappropriate in an 11+.

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