ajlelectronics
Member
- Messages
- 11,035
- Location
- Gloucester, England
- Thread starter bigegg
- Start date
JulieandTony
Member
- Messages
- 149
Yup when there is addition or subtraction, it gets a bit more important , but for simple multiplication / division the order can be flexible, as in the case highlighted
Screwdriver
Member
- Messages
- 10,902
It is worthy of explanation in terms of percentages because for a lot of people, mathematics is a foreign language. Your "explanation" was a factor of 100 wrong!
I had not even considered the idea that you could pick and choose which numerator might become the easier decimal because while 17.5% of £25 doesn't jump out at me, 25% of 17.5 doesn't look like it helps much either. FWIW, typically I'd add 1.75+1.75+ <whatever half of 1.75 is> which can be cumbersome to hold in your head. But 25% of 17.5 is marginally easier since you just halve 17.5, then halve it again, you don't need to hold the result of a sum in your head while calculating a different sum.
Everything is obvious after someone explains it and we can all be a genius behind the screen, everyone knows everything Google knows. The degree quip is in response to a couple of comments above. It takes some confidence to display to the world that you had never considered such a simple "trick" since that might just as easily be a sign you're a bit dim! I respect that level of honesty.
On the other hand, just saying "yeah that's really obvious I knew it all along" is somewhat less revealing and possibly even disingenuous.
Seadog
Save the planet. It's the only one with rum!
- Messages
- 12,963
- Location
- NE London - UK
Simple, isn't it? People could never understand how I could work it out in my head in a few seconds
JulieandTony
Member
- Messages
- 149
I didn't at any time suggest that 4 x 75 or 75 x 4 is the same as (4/100) x 75
There is no factor of 100 out.
I was merely pointing out that the order of multiplication can be reversed by way of a simpler view.
This is done all the time, who actually tries to calculate 12% of 20 by dividing 12 by 100 (=0.12) and then multiplying by 20?
I would imagine that most would just multiply 12 x 2 to give 24, then by 10 to give 240, then divide by 100 to get the answer 2.4
This is something I thought everyone is taught to do in school - basic maths in the head.
Not trying to calculate difficult numbers like 0.12 x 20, but simple steps to break it down into more manageable calculations.
Just like working out the diameter of a no 8 tig nozzle, it's 8/16, so mentally I think 4/8, then 2/4, then 1/2, and finally remember it's in inches so no 8 = 1/2" dia nozzle
JulieandTony
Member
- Messages
- 149
Some 25yrs ago it was pointed out to me why VAT (at the time) was 17.5% - mind blown!
Take ten percent, half it, half it again and add the three together.
Simple, isn't it? People could never understand how I could work it out in my head in a few seconds
Exactly!
This is the sort of mental arithmetic I was suggesting with my previous comments.
Don't try and solve a difficult calculation, solve lots of simple ones.
I thought everyone was taught this at school (I would have thought junior school - but can't remember)
ajlelectronics
Member
- Messages
- 11,035
- Location
- Gloucester, England
Not really... Take 'indoors for example. When we discussing alcohol content of beer, she read that it was 5%. Now apparently the reason that people get drunk is because two beers is 10% alcohol and so therefore 10 beers is 100% alcohol.
I tried to explain to her using percentages of 100 and 200 buttons and she could answer the questions correctly. She still can't work out the beer though.
A camping trip a few years ago required the chemical toilet to be sorted. She didn't understand the ratio for mixing with water, something like 20:1 so she poured half the bottle in.
She goes shopping and buys products like cat food at 39p per tin. That is apparently cheaper than pouches at £3 per box despite the Kilo cost being £7 and £2.50 respectively... "I haven't got time to go round looking at shelf labels". ;-)
JulieandTony
Member
- Messages
- 149
Not sure it means she wasn't taught it, but it sure looks like a case of "doesn't do maths"...
:-)
JulieandTony
Member
- Messages
- 149
I get dismayed with similar things though, like the argument that two cars hitting each other head on at 70mph is like one car hitting a brick wall at 140mph
No it ****** isn't
Each car stops travelling from 70 to zero (assuming they're the same size), so each car decelerates just the same as it would by stopping travelling from 70 to zero in hitting a wall.
The deceleration felt by a passenger in each car would be the same!
No it ****** isn't
Each car stops travelling from 70 to zero (assuming they're the same size), so each car decelerates just the same as it would by stopping travelling from 70 to zero in hitting a wall.
The deceleration felt by a passenger in each car would be the same!
pedrobedro
Man at Matalan
- Messages
- 13,088
- Location
- CX near Chesterfield
Just cut the pizza in 4 pieces, I don't think I could manage 6. That's logic not maths 
Tangledfeet
Knurling is my Nemesis.
- Messages
- 3,213
- Location
- Top of a hill above St Andrews, Fife
Simple, isn't it? People could never understand how I could work it out in my head in a few seconds
And it's even easier these days... unfortunately!
JulieandTony
Member
- Messages
- 149
Just cut the pizza in 4 pieces, I don't think I could manage 6. That's logic not maths
Good point, for the same reason, I am just about to replace my 200w guitar amp with a 75w one because the volume control goes up to a massive 11 - much better than the 10 on the old one.
(before anyone gets pedantic - it is a joke, I know 11 isn't massive - it's just 11)
Apparently this stuff is written in English, who knew?
This is similar to my wifes' technical information that she brings home from conferences, she is a medical scientist and I understand about 1-2 words in every 4-6.
Wallace
Member
- Messages
- 7,777
- Location
- Staines, Middlesex, England.
He sounds like a bully.
It's interesting when I help my kids with maths homework, one things that seems to have changed is kids don't seem to be learning how to spot patterns that help work things out.
We learned times tables at school parrot fashion till you could recite them every which way, kids don't do that anymore
Very often if you are good with numbers you are doing multiple calculations in your head without realising. I tried to get my kids to think about a question and work with what they know, they will look at 17x15 and sit and try and work it out without thinking that it's the same (10x15)+(7x10)+(7x5) which many of us would do without thinking.
You get the same issue when you give a young shop assistant an oddball amount of money so you get your change in a convenient format, totally confuses most them.
We learned times tables at school parrot fashion till you could recite them every which way, kids don't do that anymore
Very often if you are good with numbers you are doing multiple calculations in your head without realising. I tried to get my kids to think about a question and work with what they know, they will look at 17x15 and sit and try and work it out without thinking that it's the same (10x15)+(7x10)+(7x5) which many of us would do without thinking.
You get the same issue when you give a young shop assistant an oddball amount of money so you get your change in a convenient format, totally confuses most them.
Just cut the pizza in 4 pieces, I don't think I could manage 6. That's logic not maths
You probably burn more calories eating 6 due to the two extra arm movements but that's not factoring in the longer time holding the heavier pieces if you only have 4.
JulieandTony
Member
- Messages
- 149
Yup just the other day I worked out it was something like £7.20 for a few quick bits - I gave her £10 + £2 + 20p expecting to get a fiver back she just looked at me totally blank, gave me the change back and the till told her to give me £2.80 which she eventually did after trying to work out which coins she needed to pick!
rtbcomp
Moderator
- Messages
- 18,573
- Location
- Sheffield UK
Sometimes it's quicker to recognise a pattern than it is to do a calculation longhand. I don't remember most of my tables these days, for example if I want 7 * 9 I can calculate 7*9=7*10-7 = 63
Before electronic tills made things easy if you gave a shopkeeper a tenner and he was short of change he would ask for the £2-4s-0d and give you a fiver change. Sometimes I think they did it deliberately to confuse the customer and short change them.
My father was a bank clerk and his father a maths teacher. Dad could add up a column of numbers (£-s-d) quicker than the younger members of staff could use an adding machine.
Screwdriver
Member
- Messages
- 10,902
Interestingly though, all that article does is to give a high degree of probability that ATLAS had "discovered" the Higgs. It wasn't until the discovery was confirmed a couple of years later at the LHC that the scientific community were convinced.
Another interesting factlet about these gigantic machines is how they switch them off. There is a huge amount of energy in a proton beam travelling at 99.xx c so you can't just switch the thing off. After the experiment has concluded the proton beam is dumped into a huge lump of granite which absorbs the energy, dissipating it as heat.
