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

keet83

learn how to round up the price example... £9.99 = £10, and little short cuts like 33% = divide by 3 times by 2, 75% = divide by 4, 25% = divide by 4 times by 3 etc...

TigerTiger_2

So pleased that I am not the only one frustrated by modern maths teaching methods. My youngest got an A* in her maths GCSE having taken it a year early but is hopeless at mental arithmatic. Her response is that she has a calculator on her phone so doesn't need to be able to do sums in her head!

Rant over.

eileenfromplaistow

Even my sister, who only got her GCSE (showing our age now!) on the second go, can do the mental maths. I am appalled when Tesco put up an enormous chart for their "10% or 20% off" clothes sales, listing prices before, discount and "you pay". Woolworths used to do the same.
My niece, by the way, was most impressed that my daughter could convert the dimensions of her kitchen floor to "number of packs required" of laminate flooring in B&Q - she thought everyone had to get the assistant to work it out for them!

dzug1

minerva_windsong wrote: »

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!

Some of these have easier ways - for example 33% - divide by 3; 25% - divide by 4.

And I can do the shopping trolley - but forget the total after about 30 seconds, so usually don't bother

Morporkian

I answered A because, quite simply this sort of thing is easy for me.

I am much more of a "numbers person" than a "letters person". I'd be good on countdown if it didn't have the other half LOL

Anyway, as others have said, always simplify it for yourself. I had a complete "DOH" moment earlier in the year. Boots were having their 75% off sale with the remaining Christmas goodies form last year. I wanted to figure out what I was going to pay for something, so did the simply "divide by 4", but then somehow forgot that the answer I had was indeed what I needed, as it was *75*% off and not 25%. I felt silly after multiplying by 3 and then taking it away :P

As for adding up the trolley, I am usually fairly good (though managed to miss about 50p last night, even with rounding :K). When we lived in Essex the local Somerfield actually had trolleys with calculators on them for people to use. Very handy.
Not that we ever did, Mum could do it herself anyway and I would just try writing my name and various other things, as kids tend to do!

As my Grandad always said, "calculators are only any good if you know how to add up anyway". How would you know whether or not the answer was correct if you didn't know roughly what you wanted anyway?
Again when living in Essex we rarely, if ever, used calculators for Maths at school. Granted, this was year 5, so 9-10 in age, so the Maths wasn't really that bad, but regardless, we didn't use them. We did times tables every week (as well as spelling) and long division/multiplication was the norm. When we moved to Suffolk, people were terrible. They used calculators a lot, most of the kids had them and heaven forbid you should ask the to do long division/multiplication I was in shock. I couldnt understand why people had such issues. Needless to say, I rarely used a calculator.
Even when we got to GCSE/A-Level. I taught myself Standard Deviation at GCSE Level using the book and doing it all by hand. When the teacher got to it and did it with a calculator, I was baffled. I couldn't see the numbers and it was much harder to correct yourself if the answer was wrong, as you had to input everything again, rather than just look over the working and fix it - because it was obviously in pencil, not pen like people do now
Even now I don't. I will "write" the numbers with my fingers if I need to. Doing the movements helps me "see" it with bigger/more difficult numbers, but means I don't have to faff about with calculators.

My other half laughs at me when I stand in the shop working out the prices and which is better value for money. I rarely trust the labels with their 54.2 pence per 100g etc. I like to make sure - especially with Tesco and their creative adding skills!

Wow, sorry for rambling. :P

savercol

Supermarkets are not very helpful when working out the price of items. For instance, cheese. All the different cheeses will have a price per kilo in small print on their price tickets. But cuningly, special offers or own brands will have a price in small print 'price per pound' so a comparison cannot be made quickly.

Hantopcat

A - definitely

Why do you have to round up? What's wrong with 3 x £1.69?

KeithSheppard

worbikeman wrote: »

I did A-level maths at school (failed) - 2 years of simultaneous and quadratic equations, integral and differential calculus. Still dont know what they're for. I was alright until they started using letters instead or numbers. The only thing I need maths for in real life is shopping and playing darts.:rotfl:

The sample question isn't maths, it's arithmetic. There's a real difference. I have a maths degree. I have used (eg.) calculus many time in adult life but mathematicians are notoriously bad at arithmetic.

I can manipulate the formulae and love algebra, but I cannot add up to save my life. That's what computers are for.

I just about struggled through the sample question by saying it's 17 pounds, as near as darn it, then multiplying 1.7 by three. That's about on the limit of my arithmetic powers.

KeithSheppard

TigerTiger wrote: »

So pleased that I am not the only one frustrated by modern maths teaching methods. My youngest got an A* in her maths GCSE having taken it a year early but is hopeless at mental arithmatic. Her response is that she has a calculator on her phone so doesn't need to be able to do sums in her head!

Rant over.

Unless, of course, the battery runs out at the wrong moment.

I help out with numeracy in a local junior school for an hour each week and I whince every time I'm reminded of how they teach numeracy in school these days. Kids are very good at learning things by rote. If you tell a child the traditional method for doing, say, long division, most will be able to learn how to do it without necessarily understanding _why_ it works. For most people, the "why" will be irrelevant to their adult life.

The accent in schools these days is too much on understanding why numbers work the way they do. They teach kids various "strategies" for tackling numeric problems and expect each child to use the strategies they are most comfortable with. Many kids find this totally confusing and would be far better off if you told them "this is the way to do it".

I do agree with your youngest, though, that arithmetic isn't a significant part of maths once you get past a certain level (see my other posting).

OK, my rant over.

davetrousers

If you start with 100 then add 10% and then deduct 10% the answer is not 100.

Some people don't seem to understand this. It's a bit like people deducting 15% (or 17.5%) from a total price to work out the pre-VAT price.