'Can you do percentages in your head?' poll discussion

rosalie-lavender

I could do it but it would take me time. I am fine if I have a piece of paper and a pen but I struggle to work things out in my head.

ThinkingOfLinking

I'd say C. I was never great at maths; scraped through GCSEs with a C grade, but I can work out the basics. For 25% discount, I work out 10%, which I then half to make the 5%, and I add the 5% to the 10% number and add another 10% to make the 25% ITMS. But I'm not too bothered as I have a calculator on my phone of course.

minerva_windsong

For the example, I'd work out what 10% was, rounding up or down when necessary (so 10% of 16.99 is 1.699, so rounded up to 1.7), times that by three (1.7 x 3 = 5.1) and subtract from the original amount, so 16.99 - 5.1 = 11.89. For 5% I just halve 10% and add it on, so 25% of 16.99 is worked out as (1.7 x 2) + (1.7 divided by 2) = 3.2 + 0.85 = 4.05.

I can never do the shopping trolley thing though, even with rounding up!

glossyhair

I always shop with a calculator. Sure I must look like a right numpty but needs must when every penny counts!!

teddyco

The secret to doing percentages in your head is to break the percentage of the item into pieces, figure out the pieces that you know, and then add them back together in your mind.

30% of £16.99 is easier when you round it up to £17.00 and then take 10% of £17.00 = £1.70...........then multiply by 3 = £5.10
So an item in the store that is £17.00 @ 30% discount has a total price of approximately £11.90.

The other way is to break the amount into pieces rather than the percentage. So for example: I don't know what 30% of £17.00 off the top of my head, but I do indeed know what 30% of £10.00 is and that's £3.00. I also don't know what 30% of £7.00 is, but I do know that 30% of £1.00 is £.30 pence. So I take £.30 pence and multiply that by 7 to get £2.10. Then add the parts back together and that's £3.00 + £2.10 = £5.10.....now subtract that from the original price of £17.00 and the discounted price of the item is £11.90.

It's like riding a bike; If you have never done it before, then it seems difficult, but after you train your mind to do it, it's as easy as falling off a log.

DdraigGoch

I voted B, despite having "achieved" an E in Maths - which was when an E meant that you probably spelled your name wrong! I agree that decimalisation has made money maths so much easier.

scotsbob

I can do most percentages in my head.

That is because I went to school in the 1950s and at the age of 10 the teacher gave us a good belting if we didn't know them all mentally.

If I went to school today I would probably need to progress to maths at university level to know what a percentage was.

jax1305

A.
i find this kind of thing quite straight forward so it puzzles me why some users seems to go to such lengths to confuse themselves! teddyco - why break the amount into pieces when the first method works fine? the more times you chop and change things and the more sums you do to get to the answer, the more room there is for error. minerva-windsong - what is wrong with dividing by 4? its the same as 25% (as in, if you have 100% and divided it into four pieces each would be 25%). you have ended up with the wrong answer, 25% of £17 is £4.25 (half it and half it again)
schools seem to now use these lengthy crazy ways of doing sums. what is wrong with things like long multiplication and division? they work fine and its straight forward. now its grid methods and partitioning, doing ten times as many sums as you need to, adding them up and hopefully getting it right. aaarrgh!

Thebiguglyone

jax1305 wrote: »

A.
i find this kind of thing quite straight forward so it puzzles me why some users seems to go to such lengths to confuse themselves! teddyco - why break the amount into pieces when the first method works fine? the more times you chop and change things and the more sums you do to get to the answer, the more room there is for error. minerva-windsong - what is wrong with dividing by 4? its the same as 25% (as in, if you have 100% and divided it into four pieces each would be 25%). you have ended up with the wrong answer, 25% of £17 is £4.25 (half it and half it again)
schools seem to now use these lengthy crazy ways of doing sums. what is wrong with things like long multiplication and division? they work fine and its straight forward. now its grid methods and partitioning, doing ten times as many sums as you need to, adding them up and hopefully getting it right. aaarrgh!

Totally agree with this one- 25% is 1/4. much easier.

The school thing also... does my head in trying to help my daughter with the new method. Keep finding myself saying "It's much easier if you were to do it this way...!"

jenniewb

I can! I do it all the time- to compare prices- say one item is priced at normal price, then you get a multipack- I want to know what percentage I am saving if I get the multipack- is it worth my arms carrying them back..etc etc. Daily I do this sort of thing in shops. Its been that way for about 7 years or so now and the more you use your head like this, the better you become.

I agree with the idea that 10% is the key, and then 1% for all the additional bits- say trying to work out 87% or something. Always work to or from the nearest 25%, its easy to divide by half and then half again (more then this you can get yourself confused as to how many times you divided) then just take mini steps to work your percentage from there.

For working out the percentage of something, its a division thing- you become better at it in time, then multiply by 100 to get the end result/percentage figure.

I'd give myself a B for that, because I'd still have to stand around calculating. I did study 11 of the 12 units for A-Level maths, got ill, missed a unit of the exam and had to take the AS level, ended up with a B. But that was about 10 years ago! I did an art degree after that- you need maths for that believe it or not, lots and lots of calculating (dyes, colours, yarn, thread, weights, times...), you do it wrong, you goota start a whole precedure again. Maybe thats why its also important!