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ds in year seven is throwing a ruckus about the area of a circle

(29 Posts)
stitchtime Tue 26-May-09 16:03:03

he is being ridiculous, and not accepting that he needs to know how to work out the area of a circle, using pi x radius squared.
can a teacher please tell me to that kids have covered how to work out the area of a circle using pi, coz he is being ridiculous, and saying it is a level stuff

oopsacoconut Tue 26-May-09 16:09:14


pi x r2

pi is 22/7
so 22 divided by 7 times radius squared
first square radius the multiply by the answer you get by dividing 22by7.

does that make any sense?

foxytocin Tue 26-May-09 16:09:44

I am a teacher and yes, everyone gets to learn the area of a circle and you always use pi x radius squared. there is no other way.

and when you do know how to do this it will seem so easy you will be shamefaced wondering what all the fuss was about.


margotfonteyn Tue 26-May-09 20:19:57

Just asked DS2, Year 8, said def knows that but when questioned closely said learnt in Yr 8 but could have poss learnt it in year 7, but teacher 'was crap' so may not have understood it!!! Complete apologies to all teachers, his words not mine, but may explain OP's sons 'ridiculousness'. Hope this helps, rather than hinders.(btw is at grammar school).

IotasCat Tue 26-May-09 20:23:59

Ds1 yr 5 state primary knows this

SoupDragon Tue 26-May-09 20:25:55

I didn't think there was another way to work out the area of a circle.

I certainly learnt it well before I took A level.

stitchtime Tue 26-May-09 21:28:33

thats what i thought too. he was being asked to work out the density of a telegraph pole, and was given its mass, height, and the radius of the telegraph pole, afaik there is no other way of doin git. but he was just throwing such a tantrum about it.
sad takes up more energy than the work he needs to do

foxytocin Wed 27-May-09 08:38:12

i think i learnt area of a circle in about yr 5 too but that was a looong time ago and overseas.

will ask dh if using pi / area of circle has any place in his line of work. (deals with lots of maths)

foxytocin Wed 27-May-09 08:58:17

this is what dh said:

pi is everything!

What is there not to learn-it is one of life's constants and as such is indispensible!

there. from someone who is into building bridges, roads and rails, powerstations...

(he may have to come back and qualify the second sentence methinks.)

foxytocin Wed 27-May-09 08:59:17

"pi is everything!

What is there not to learn-it is one of life's constants and as such is indispensible! "

forehead Wed 27-May-09 10:10:50

pi= 3.142
area of a circle = pi multiplied radius squared.
When one learns this could depend on the school. I learned this at the age of 11 but i know some children learned this at 14 years old.

stitchtime Wed 27-May-09 10:35:20

thanks foxy he has been TOLD

ArcticLemming Wed 27-May-09 10:43:44

At the age of 44 I've just used this for the first time in real life to work out how much bark I need to buy to cover a circular flower bed. Maybe if you explain the practical application he's suddenly be enthused hmm

bloss Wed 27-May-09 10:47:24

Message withdrawn

ellingwoman Wed 27-May-09 10:52:38

I first learnt it in year 7 (1968) I couldn't grasp it. What does it mean? Why is it called pi? What is so magical about 3.14? Did I have to know how it was worked out to be able to use it correctly?

I think if my maths teacher had explained it's just a constant etc I may have 'got' areas instead of worrying about something I wasn't clear on using.

Does that make sense? grin

<shivers at memory of 'volume and density' chapter in maths book>

foxytocin Wed 27-May-09 11:34:13

more from DH

"pi is a constant

I learnt to use 22/7 at school but that is only an approximation which is easy to remember

22/7 = 3.1428571etc whilst true pi is 3.1415926 etc

Of course some people get by without understanding or ever using pi-but they would tend to be people who have jobs where they don't have any freedom/or want to think for themselves. (Foxy never uses pi herself but then she teaches french, spanish and english for a living grin)

I use pi constantly both forms and so does anyone working out how much material they want. XXXX (DH's good mate) works out areas so he can get the right volume of paint for circular tanks etc."

GrapefruitMoon Wed 27-May-09 18:09:19

I do worry what exactly they are teaching them in maths these days - I thought there was a drive some time ago to go back to basics?

DD had a test recently and came home to say she couldn't work out 3/8 as a decimal. She was astounded when I told her it was 3 divided by 8 and showed her how I worked it out in my head (maybe it would have been easier to work out that 1/8 is 0.125 and multiply that by 3 - but then she wouldn't know how to do more "tricky" ones.)

I blame the over-use of calculators myself [old fogey emoticon]

bloss Wed 27-May-09 19:45:23

Message withdrawn

GrapefruitMoon Wed 27-May-09 20:21:05

Don't get me started on multiplication! I really wish they would go back to teaching times tables by rote in primary - such a useful piece of knowledge to have.

stitchtime Fri 29-May-09 12:11:19

mulitplication tables..... dont get me started on those. ds2 knows them all. coz i have made sure he does. by rote. but the child still doesnt 'get' them. why is 5 x6 30 ? he doesnt understand it. but he is not even 8 yet. so i am hoping ot be able todrill it into him by then.

summer111 Tue 02-Jun-09 19:34:18

For what it's worth, dd (Yr 7 ) is in one of the top maths sets and when asked, said that they haven't covered the area of a circle yet. Hadn't ever heard of pi!

wahwahwah Tue 02-Jun-09 19:35:20


And my dad was a maths lecturer at uni.

Goblinchild Thu 04-Jun-09 07:41:05

Stitchtime, as well as teaching him by rote, teach multiplication as arrays and grouping, Use real money, that way you get his attention too.
GrapefruitMoon, we do teach them by rote in school, it's one of the strategies. You could wander around and hear the chanting of tables any day in my place of work.
Our Y5/6 cover areas of circles and volumes of cylinders.

SofiaAmes Thu 04-Jun-09 08:25:18

Here in usa they learn times tables by rote in 3rd grade. But I am not so happy with the lack of underlying fundamentals. I don't think that the kids really understand that multiplication is just a quick way of adding. And they don't learn how to visualize the addition and multiplication. And they have started doing these awful timed tests which just irritate the hell out of me because apart from there being no studies at all that show that they are beneficial in any way, they encourage the kids to go quickly at all costs (as long as you get most of them right) instead of slowly and accurately, which is how I was always taught to do math.

SofiaAmes Thu 04-Jun-09 08:27:54

Many years ago when I was a kid, I used to hang out with nerds in middle school and they would spend lunchtime bragging about how many place of pi they had memorized. Me, I can't even remember the phone number and address at work and I've been there for 1.5 years!

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