The school maths question dividing the internet

Forums › Off topic › The school maths question dividing the internet

1 | 2 | 3 | 4 | 5

Jaxson

8044 posts

Uber Geek

Trusted

#1422050 5-Nov-2015 23:11

MadEngineer: It's not a square.

108m^2 is the total area of the whole shape.

Regardless of being a square or not, it's areas is still one side multiplied by the other.

It's shown close to a square in the demo drawing, so not enough to get worked up over.

eracode

Smpl Mnmlst
8872 posts

Uber Geek

ID Verified

Trusted

Subscriber

#1422083 6-Nov-2015 03:03

LennonNZ: long story.. but..

there are 2 answers...
12 and 36

Lets work it out..

Rectangle and Triangle

d(12−0.5d)+2(0.5(0.5d(0.5)d))=108
−0.25d2+12d−108=0

Use some quadratic formula (a little hard to display here)

d=12 and 36

Of course the image is nothing like that the imaginary shape as the triangle has a negative size or the rectangle does.

(or I got it complete wrong) :-)

The solution of the quadratic equation

d^2 - 48d + 432 = 0

which represents the total area of 108 m2, is:

(d - 36)(d - 12) = 0

and therefore d = 36 or 12.

Sometimes I just sit and think. Other times I just sit.

eracode

Smpl Mnmlst
8872 posts

Uber Geek

ID Verified

Trusted

Subscriber

#1422085 6-Nov-2015 03:33

MadEngineer: I had this question from when I studied NZCE

F*** you Envelope. I never liked letters anyway.

Sometimes I just sit and think. Other times I just sit.

evnafets

537 posts

Ultimate Geek

Lifetime subscriber

#1422155 6-Nov-2015 08:54

And to finish off stating the obvious. The equation has solutions of d = 12, or d = 36

However you can also determine from the diagram, the constraint of 12 - d/2 > 0.
Using d = 36 gives you a negative result for that equation, therefore d=12 would be the correct answer for this question.

MadEngineer

4295 posts

Uber Geek

Trusted

#1422512 6-Nov-2015 16:32

Jaxson:
MadEngineer: It's not a square.

108m^2 is the total area of the whole shape.

Regardless of being a square or not, it's areas is still one side multiplied by the other.

It's shown close to a square in the demo drawing, so not enough to get worked up over.

i added the statement for clarity. Some people get worked up over nothing ...

You're not on Atlantis anymore, Duncan Idaho.

Kyanar

4089 posts

Uber Geek

ID Verified

Trusted

#1422531 6-Nov-2015 17:12

"That exam wasn't there to test us, it was to trick, no one could of prepared for that," another VCE student wrote.

This student should probably spend a bit more time studying at school, rather than complaining about the content.

hashbrown

463 posts

Ultimate Geek

#1422540 6-Nov-2015 17:42

I suspect the envelope problem is a good question that got mangled. If you make the bottom side of the "square" 12-d/4, the d^2 terms cancel and you are left with 12d=108, so d=9. As an added bonus the "square" is now 9x9.75 which is believable for the way it was drawn.

Obviously the total length is now 12+d/4, but it was weird they gave you that redundant info in the first place.

Sharesies

Trade NZ and US shares and funds with Sharesies (affiliate link).

Sideface

9363 posts

Uber Geek

Trusted

Lifetime subscriber

#1422783 7-Nov-2015 11:53

andrew027:

I thought that this was a silly question until I saw this:

Suzuki Microbus-like van

Sideface

PeerCover

6 posts

Wannabe Geek
Inactive user

#1422996 7-Nov-2015 22:41

I briefly read the article but then realized it was an Australian 50 cent coin. I think referring to Australian currency really threw the Australian students. After all, how can one make sense of the $2 being smaller than $1, the 20 cents being bigger than both the dollars and the 50 cents being the biggest of all the coins. It defies logic. Now they want students to apply geometry to these illogical manifolds - tough ask!

andrew027

1286 posts

Uber Geek

#1423443 9-Nov-2015 08:42

PeerCover: I briefly read the article but then realized it was an Australian 50 cent coin. I think referring to Australian currency really threw the Australian students. After all, how can one make sense of the $2 being smaller than $1, the 20 cents being bigger than both the dollars and the 50 cents being the biggest of all the coins. It defies logic. Now they want students to apply geometry to these illogical manifolds - tough ask!

But the NZ 50c is bigger than the NZ $1 coin so size is not necessarily relevant.

I was living in Australia when the $2 coin was first issued in 1988 - I remember a nice cartoon of then-treasurer Paul Keating explaining to a reporter that the $2 was smaller than the $1 because two dollars was worth less in 1988 than one dollar was in 1984 (when the $1 coin was released).

And the old joke why a UK 50p coin is shaped the way it is - so you can use a spanner to remove it from a Scotsman's hand.

Kiwifruta

1423 posts

Uber Geek

ID Verified

#1423859 9-Nov-2015 16:32

andrew027: I still remember from high school geometry (and it has been 38 years since I did high school geometry) that the exterior angles of a polygon add up to 360°. The 50c piece has 12 angles, so 360÷12=30. There are two 50c pieces side-by-side, so the angle at the point the two coins meet is 2×30=60°. For kids who should have learned this stuff within a year or two of sitting the exam, I'm surprised at all the fuss it has created.

I think the fuss reflects the sheer amount of people who did not pay attention during maths class. Fairly basic geometry question.
Personally, I think the question would have been better without multi choice to take away the 'look at the picture and take an educated guess as to what the angle looks like'.

gzt

17157 posts

Uber Geek

Lifetime subscriber

#1423980 9-Nov-2015 20:28

8 sided polygon gives a direct answer, but method one was my first choice.

Batman

Mad Scientist
29769 posts

Uber Geek

Trusted

Lifetime subscriber

#1424006 9-Nov-2015 21:30

Missus says (the other day) angle of the something something = ~~360/number of sides of polygon~~, x2.
wow ... who's the smart one in the family!

ok i can't remember her exact formula ... but sometihng like that. i will ask her again at some stage ..

ok i think that was right. whatever! lol

gzt

17157 posts

Uber Geek

Lifetime subscriber

#1424118 10-Nov-2015 08:28

gzt: 8 sided polygon gives a direct answer, but method one was my first choice.

Oh wait I had that confused with a six sided regular polygon. : (.

Kiwifruta

1423 posts

Uber Geek

ID Verified

#1424164 10-Nov-2015 09:49

joker97: Missus says (the other day) angle of the something something = ~~360/number of sides of polygon~~, x2.
wow ... who's the smart one in the family!

ok i can't remember her exact formula ... but sometihng like that. i will ask her again at some stage ..

ok i think that was right. whatever! lol

where n is the number of sides
180-360/n, which can be rearranged to 180x(1-2/n)

1 | 2 | 3 | 4 | 5