This video covers how to calculate the original value of an item after it’s increased or decreased by a certain percentage. For example if a pair of sunglasses has 20% off and now costs £56, what was the original price before the discount? We often call this topic reverse percentages.

This video is suitable for maths courses around the world.

KS3 – Not on your course

GCSE Foundation – All on your course

GCSE Higher – All on your course

A-level – Basic for your course

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https://www.youtube.com/watch?v=aHVJfRxeAxo&list=PLidqqIGKox7UVC-8WC9djoeBzwxPeXph7

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If you’d like to practise the material covered in this video, check out our platform at http://www.cognitoedu.org – it's totally free, and has been built to make learning and revision as easy as possible. The main features are:

– Lessons organised by topic, only the lessons relevant to your specific exam board and tier are shown.

– Automatic progress tracking. Progress bars tell you what you’re doing well at, and what you need to spend some time on.

– Practise quizzes so you can test your knowledge. You can quiz yourself on any combination of topics you like.

– A huge number of fully-hinted questions that take you step-by-step through some of the trickiest calculations & concepts.

– A comprehensive bank of past exam papers, organised both by year, and also by topic.

Amadeus & Tom

i have math exam tomorrow and you just saved me

Thnk u it has really helped

Thanks cuz I got paper 3 mocks tommorow morning at half 8 you prob just saved me a few marks g

TYSM

I’m helping my daughter with her gcse (she isn’t at school in England but has to do it for an upcoming move). I’ve never been able to do maths and my daughter hates it. But we LOVE this channel. It’s the only one makes any sense. Brilliant ❤

What the heck. It can't be made easier than this. Thank you! You're so pro!

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i have a math exam in a week and i’m panicking. it’s safe to say that you just saved my life and sanity, thanks!

Question:

The price of a mobile phone increases by 15%.

The price of the mobile phone after the increase is $391

What was the price of the mobile phone before the increase?

The marking scheme says you only do 391÷1.15=340

They never divided by 100 so I am confused

This is so helpful. I literally don't understand a thing my math teacher taught me.😭

shit video

Thank you!

Thank you so much for making these types of videos. TRUST ME it has helped me SO much in my exams. Your channel is the only channel i go to for revision. THANK YOU!

@Cognito can u upload a video on upper and lower bound

So helpful for my maths test tmrw tysm

amazing video!

, thank you so much wala God of math

This is wayy better than those big ass formulas

Thanks~!

You are pro

PSA for anyone who conceptualizes these problems from a different angle here is a different way to get the same answers (of course the way in the vid is completely valid this is just an alternative).

If you think of the percentages as pure decimals you can often cut a few steps. For example the first problem where the house is increased by 15% to £207,000. Your target is the original 100%. So you can do it in one step by taking £207,000/1.15=£180,000.

Same method for example 2: 20% sale with new price at £72.00 (100% OG price the target again). So this time you’d take £72/0.80=£90.00.

Only one that is a tad counterintuitive is the one where you are given the % and the change in price but neither original nor new total. In that case you take that price change (delta) and divide it by the % given in decimal form (sounds complex but really easy in practice). So for the example problem 5% increase=£42.50.

Take £42.50/0.05=£850. Then finally since 850 is the OG price you’d add that £42.50 on top for the £892.50 new price. Lastly to drive the point home let’s say that problem was the same but it was a decrease/discount instead. Everything would be the same save the last step where you’d subtract the 42.5 from 850 in the end.

Side note with any problem like this it’s easy to accidentally flip things around so a good practice is to mentally check yourself as you go by asking if the number you just got makes sense. Like if you multiply the first problem by 1.15 instead of dividing it. You end up with a number higher than the 207k you started with (which makes no sense lol).

I doubt anyone will have read all that but if by some miracle you did and it helped lmk lol 😊

i hope we can get rid of all the teachers in the world all replace them with people like you

For the first question, you can do £207,000 / 1.15 to get £180,000.

Thankyou, I've just started a new job and have had to dust off the back of my brain 😁

Love your channel it has very effective explanations, obviously I understand more than school

The fact that you explain why each step is the way it is and how it relates to the funtion and not just show me how to solve it, is exactly what I needed. Thank you so much for this you are a life saver.

I get it now!!

I understood it here more than in school !?

not a student but I found this very helpful. Thankyou.

Clearly and easily explained. Thank you, Sir!

Thanks for the video

And the 300k ❤️🎉🎉🎉🎉🎉🎈🎉🎉🎈🎈🎈🎈🎉🎉🎉🎉🎈🎉🎈🎉

will be giving my gcse in 2023 love this such a simple but effective method of explaining happy that i have found you

thanks

thank this will help for my next maths test

Thank you so much for this 💗 💖

ngl ur great u explain what a 80 minute lessson explains in like 10 mins

Thanks, needed a refresh.

what if we know the original price and we need to use the percentage increase or decrease to solve the new price?

3:03 revising for a progress check in y9 set 1 rn lol they give us gcse papers, and why is a pair of sunglasses £72 lol thats a ripoff just saying

CONGRATULATION YOU JUST HIT 200 K SUBS OMG

This channel is one of the best .im so glad I came across this.its so helpful.many thanhsssss

i have a test tomorrow and this video really made it simple for me so lets just say it got me a few marks back

my teacher confused me as we'd use both diving by like 1.1 and I'm very confused still but this method is easier for me

Tysm! this way is better

Nice I was struggling in maths

if it took 57 seconds to do something. now it takes 11 seconds to do that.

to find the % of how much better it is. do i 57/11×100? =518% more efficient ?

or is that wrong? sorry it's been a while since i did much math. appreciate any help.