Geometry Question

The whole reason for the selfsufficientish website was to offer a place where anyone can ask, HOW DO I...? So who knows why it has taken us so long to have a HOW DO I? section, but here it is. So if you want to know how to do anything selfsufficientish then here is the place to ask.

Geometry Question

Postby Crickleymal » Sun Dec 16, 2012 9:19 pm

Ok not a self sufficiency question, but there must be some mathematicians here. Normally I'm good at maths but for some reason this one has me stumped.

GCSE practice paper.
Sum of angles in a polygon of n sides = 180n-360.

A polygon has 2 corners with internal angle 90 degrees. The remaining corners all have angles (internal presumably) of 144 degrees. How many sides does the polygon have?
Malc

High in the sky, what do you see ?
Come down to Earth, a cup of tea
Flying saucer, flying teacup
From outer space, Flying Teapot
Crickleymal
Living the good life
Living the good life
 
Posts: 260
Joined: Wed Aug 17, 2011 1:16 pm
Location: Gloucester

Re: Geometry Question

Postby GeorgeSalt » Sun Dec 16, 2012 10:16 pm

Sum of angles = 180n - 360 = 180(n-2)

2(90) + (n-2)(144) = 180n - 360
180 + 144n -188 = 180n - 360
352 +144n = 180n
352 = 36n
9.778 = n ???

Something not riight there.. but I cant see where I'm going wrong.. how have you tackled it?

Just in case, 180 - 144 = 36

2(90) + (n-2)(36) = 180n - 360
180 + 36n - 36 = 180n - 360
504 = 144n
3.5 = n

From dragging around the irregular polygon points on this page I know the answer should be 7. I can't get it to work though.. too late tonight I suspect. I'll look again tomorrow.
Curently collecting recipes for The Little Book of Liqueurs..
GeorgeSalt
Living the good life
Living the good life
 
Posts: 425
Joined: Sat Apr 28, 2012 10:21 am
Location: West Norfolk, UK

Re: Geometry Question

Postby GeorgeSalt » Sun Dec 16, 2012 10:36 pm

Ok.. I can get it to work backwards, so it's a simple error somewhere..

180n - 360 = 720 <-- for n=7
720 - 90 - 90 = 720
720 / 5 = 144

I see the error I've made..

2(90) + (n-2)(144) = 180n - 360
180 + 144n - 288 = 180n - 360
180 - 288 + 360 + 144n = 180n
252 +144n = 180n
252 = 36n
7 = n

There you go..
Curently collecting recipes for The Little Book of Liqueurs..
GeorgeSalt
Living the good life
Living the good life
 
Posts: 425
Joined: Sat Apr 28, 2012 10:21 am
Location: West Norfolk, UK

Re: Geometry Question

Postby Crickleymal » Mon Dec 17, 2012 8:46 am

Thanks. I had a brainwave last night about 11:30 and that is the exact reasoning that I came up with.
Malc

High in the sky, what do you see ?
Come down to Earth, a cup of tea
Flying saucer, flying teacup
From outer space, Flying Teapot
Crickleymal
Living the good life
Living the good life
 
Posts: 260
Joined: Wed Aug 17, 2011 1:16 pm
Location: Gloucester

Re: Geometry Question

Postby marshlander » Tue Dec 18, 2012 12:58 am

Is this you?
Attachments
i_hate_math_will_make_you_mad5.jpg
(20.17 KiB) Downloaded 684 times
imagesCAPOWEB2.jpg
imagesCAPOWEB2.jpg (6.38 KiB) Viewed 882 times
Terri x
“I'd rather be a little weird than all boring.”
Rebecca McKinsey
User avatar
marshlander
A selfsufficientish Regular
A selfsufficientish Regular
 
Posts: 1323
Joined: Tue Jan 15, 2008 2:45 am
Location: Cloddygate Farm, North Linconshire coast.

Re: Geometry Question

Postby GeorgeSalt » Tue Dec 18, 2012 9:33 am

It's only GCSE algebra (algebra hidden within a geometry question).. .. and that's a very useful type of question to be able to solve for an -isher (maybe not the polygon example).


Your homework for tonight, all working must be shown ;)

If 1lb of raspberries and 1lb of sugar makes three 10oz jars of jam, how many raspberries and how much sugar do I need to fill a dozen half-pound jars?

If 5lb plums and 3lb sugar makes a gallon of plum wine, how much wine can I make with 12lb and how much sugar will I need?
Curently collecting recipes for The Little Book of Liqueurs..
GeorgeSalt
Living the good life
Living the good life
 
Posts: 425
Joined: Sat Apr 28, 2012 10:21 am
Location: West Norfolk, UK

Re: Geometry Question

Postby Crickleymal » Tue Dec 18, 2012 11:15 am

Relatively easy too. 2lb of ingredients (32oz) molishes 30oz jam. so 1 oz of ingredients makes 30/32oz or 15/16oz. You want to fill 12 8oz jars or 96 oz. so you need 96/(15/16) which is 102.4 oz of ingredients or 3.2lb rasberries and 3.2lb sugar.
Malc

High in the sky, what do you see ?
Come down to Earth, a cup of tea
Flying saucer, flying teacup
From outer space, Flying Teapot
Crickleymal
Living the good life
Living the good life
 
Posts: 260
Joined: Wed Aug 17, 2011 1:16 pm
Location: Gloucester

Re: Geometry Question

Postby marshlander » Tue Dec 18, 2012 2:21 pm

Depends how many raspberries I eat before they get to the pot!
Terri x
“I'd rather be a little weird than all boring.”
Rebecca McKinsey
User avatar
marshlander
A selfsufficientish Regular
A selfsufficientish Regular
 
Posts: 1323
Joined: Tue Jan 15, 2008 2:45 am
Location: Cloddygate Farm, North Linconshire coast.

Re: Geometry Question

Postby GeorgeSalt » Tue Dec 18, 2012 2:25 pm

marshlander wrote:Depends how many raspberries I eat before they get to the pot!


I can add a variable for that if it would make it any easier.. .. .. ;)
Curently collecting recipes for The Little Book of Liqueurs..
GeorgeSalt
Living the good life
Living the good life
 
Posts: 425
Joined: Sat Apr 28, 2012 10:21 am
Location: West Norfolk, UK

Re: Geometry Question

Postby Crickleymal » Tue Dec 18, 2012 7:28 pm

I remember on one training course (on a radiotherapy machine) one of the test questions at the end was "How many screws have to be taken out to remove the finger guard plates?" The answer could be 44 or "too many" depending on how lenient the marker was.
Malc

High in the sky, what do you see ?
Come down to Earth, a cup of tea
Flying saucer, flying teacup
From outer space, Flying Teapot
Crickleymal
Living the good life
Living the good life
 
Posts: 260
Joined: Wed Aug 17, 2011 1:16 pm
Location: Gloucester


Return to How do I??

Who is online

Users browsing this forum: No registered users and 1 guest


.






Ishers books

Adverts (paying the bills)


Find Selfsufficientish on facebook