Maths questions

"A club committe makes 14 litres of lemon drinks for refreshments, they mix lemon concentrate to water with the ratio 2:5

How many litres of lemon concrentrate do they use ?"

2
3
4
5

I am stuggling to understand how you would work this out, is there a easy method you can describe ?

:)
 
nightrider1470 said:
"A club committe makes 14 litres of lemon drinks for refreshments, they mix lemon concentrate to water with the ratio 2:5

How many litres of lemon concrentrate do they use ?"

2
3
4
5

I am stuggling to understand how you would work this out, is there a easy method you can describe ?

:)
Click to expand...

Okay so because the ratio is 2:5 there are 7 'parts' in total.
14 / 7 = 2, so each 'part' is equivalent to 2 litres

2 parts of lemon concentrate in the ratio, so 2 * 2 = 4 litres of lemon concentrate

Make sense? :)
 
I would just do it in my head, I've never actually considered a proper mathematical method.

This seems to work however after some experimenting..

Take the total quantity being made, and divide it by the sum of the numbers in the ratio. Multiply the part you're trying to find by the number you get. In this example it's the lemon concentrate, so you take the first part of the ratio, 2.

So take your ratio of 2:5 and add the 2 and 5 together to make 7, then 14/7 = 2.

Then 2*2 = 4.

:edit: Much better explanation up there ^ - I'm certainly no teacher I tell ya :D
 
" material for dressmaking is sold by the metre. The cost of 5 metres = £17.50

What would the cost of 8 metres be ?

£22.50

£28.00

£32.00

£29.00

I understand with this question I need to devide 5 by £17.50 then x 8 = £28 :)

I was unsure how to do the 5 devided by £17.50 with pen to paper though, as it doesnt seem to work via the way I have recently learnt

Is there some easy way to do it as the .50 confuses me a little, but am sure with some rule it would be easy ?

:)
 
It's £17.50 divided by 5, not the other way round :)

You do it in exactly the same way as any other division. Just make sure you keep the decimal point in the right place. 175 divided by 5 is 35 so 17.5 divided by 5 is 3.5

175 divided by 2 is 87.5 so 17.5 divided by 2 is 8.75 and so on.
 
Mr Jack said:
It's £17.50 divided by 5, not the other way round :)

You do it in exactly the same way as any other division. Just make sure you keep the decimal point in the right place. 175 divided by 5 is 35 so 17.5 divided by 5 is 3.5

175 divided by 2 is 87.5 so 17.5 divided by 2 is 8.75 and so on.
Click to expand...
I know he wrote it the wrong way around, but since he got the correct answer I would suspect he actually did the maths correctly ;)
 
I understand with this question I need to devide 5 by £17.50 then x 8 = £28
Click to expand...

I think you have done the right sum but then written it down wrong. The fact you have arrived at the right answer suggests you did actually do (17.5/5)*8 rather than (5/17.5)*8 which is what you wrote

Sounds like you are getting on fine.

EDIT: Ninja'd
 
nightrider1470 said:
" material for dressmaking is sold by the metre. The cost of 5 metres = £17.50

What would the cost of 8 metres be ?

£22.50

£28.00

£32.00

£29.00

I understand with this question I need to devide 5 by £17.50 then x 8 = £28 :)

I was unsure how to do the 5 devided by £17.50 with pen to paper though, as it doesnt seem to work via the way I have recently learnt

Is there some easy way to do it as the .50 confuses me a little, but am sure with some rule it would be easy ?

:)
Click to expand...

17.50 divided by 5 is the same as 175 divided by 50.

So if you are trying to figure out 17.50/5 just multiply the whole thing by 10 and keep multiplying by 10 until you get rid of the decimal. So

If you start with 17.50/5
times the whole thing by 10 once you get 175/50

Another example if you got 15.25/0.5

Times the whole thing by 10 you get 152.5/5

Times the whole thing again you get 1525/50

Or you could have just multiplied by a 100 to begin with in which case you'd move decimal 2 digits to the right.

Helped?
 
Easiest way to divide 17.5 or similar by 5 is to recognise that 17.5 is 15 + 2.5 and divide both of them by 5 then add the results together. In this case, 15/5 is 3 and 2.5/5 is 0.5 so the answer is 3.5

Most division can be made much simpler by following techniques similar to this, find the largest number (smaller than the one you want to divide) that is an easy multiple of what you want to divide, then you only have to do an easy division and an easier division.
 
Judgeneo said:
Most division can be made much simpler by following techniques similar to this, find the largest number (smaller than the one you want to divide) that is an easy multiple of what you want to divide, then you only have to do an easy division and an easier division.
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I think that's true when trying to do mental arithmetic, but with pen and paper I'd just do it out longhand.
 
i round up in my head, 5 @ 17.50 i see as 10 @ 35.00 then take the 0 off so £3.50 a meter X 8
having to write down the stuff sucks lol
 
Energizer Bunny said:
Indeed. It's in my head or on a calculator. I can't even remember the last time I wrote out long multiplication or division. To be honest I'm not even sure I can remember how to do it any more.
Click to expand...

If you want to pass any exam you have to show all your working out on paper, just writing the answer, even if it's right won't get you good marks :D
 
Energizer Bunny said:
Indeed. It's in my head or on a calculator. I can't even remember the last time I wrote out long multiplication or division. To be honest I'm not even sure I can remember how to do it any more.
Click to expand...

Different types of calculators will give different answers for arithmetic.

Eg,

2x2+2x2+2x2+2x2 will give 92 on a normal cheap calculator, a scientific or graphics calculator will give 16 (which is correct).
 
If you want to pass any exam you have to show all your working out on paper, just writing the answer, even if it's right won't get you good marks
Click to expand...

In school yes. A lot of professional qualifications don't give you jack for the workings. You get the answer or you don't.

Different types of calculators will give different answers for arithmetic.
Click to expand...

Well yes but that's presumably also true of long multiplication. You will get a different answer depending on what stages you do the calculation in. Knowing how to use your calculator correctly is part of the skill.
 
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