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Im currently doing GCSE maths and the current topic is ratios. Im comfortable sharing a value between ratios but im confused by questions like

Increase £30 in the ratio of 5:2

My materials arent very clear and its frustrating me, could someone please explain the method for calculating this type of answer?

iNoob
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    speaking as someone who has taken GCSE maths (A* grade) this is probably saying "multiply by 5/2", but i'd need to see the full question to be sure, if you'd care to share in a separate discussion i'd be happy to explain it – Alex Robinson Mar 28 '17 at 20:01
  • That is the full question :) and yes you are correct, i had a brain fart a moment ago and the method is now obvious looking at the material. However I do struggle understanding the reasons behind methods. That causes me to over think things rather than just carry out the method. – iNoob Mar 28 '17 at 20:03
  • another example is Decrease 75cm in the ratio 2:3 so 75 x 2/3 = 50 – iNoob Mar 28 '17 at 20:04
  • Hi iNoob. Remember to upvote (and in some cases accept) answers that you found helpful. Thanks :) – Leo 254 Mar 28 '17 at 20:31

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I think what they are thinking is:

(new number of pounds):(old number of pounds)::5:2

Or in words: the ratio of the result to the starting value should be the same as 5 to 2.

So if our result is X, we have $$\frac X{30} = \frac52$$

Multiply both sides by 30 to find X.

Leo 254
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