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 Post subject: Maths Question - Teacher incorrect?Posted: Thu Nov 04, 2010 8:35 am

Joined: Thu Apr 23, 2009 10:00 pm
Posts: 35
Daughter's teacher has given this question and supplied answer that I believe to be incorrect. Be interested to have any expert opinions (won't give you teacher's answer or mine yet so as not to lead you down one path or another).

Q. How many panes of glass 35cm x 25cm can be cut from a sheet of glass 1m x1m?

Many thanks!

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 Post subject: Re: Maths Question - Teacher incorrect?Posted: Thu Nov 04, 2010 8:46 am

Joined: Mon Jun 18, 2007 2:32 pm
Posts: 6966
Location: East Kent
just quickly would say 10

you can get 4 x25cm from 1m, but only 2 of the 35cm from 1m width

there is a long strip of 30cm by 1m, you can cut 2 more from this

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 Post subject: Re: Maths Question - Teacher incorrect?Posted: Thu Nov 04, 2010 11:39 am

Joined: Fri Oct 12, 2007 12:42 pm
Posts: 3813
I agree with yoyo. These types of problems are easiest when drawn. Will you tell us the answers now?

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 Post subject: Re: Maths Question - Teacher incorrect?Posted: Thu Nov 04, 2010 12:36 pm

Joined: Mon Aug 02, 2010 11:35 am
Posts: 20
11

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 Post subject: Re: Maths Question - Teacher incorrect?Posted: Thu Nov 04, 2010 12:42 pm

Joined: Thu Apr 23, 2009 10:00 pm
Posts: 35

I too came up with 10 - after drawing a diagram.

The teacher has told them to divide 10000 sq cm by 875 sq cm (10000 sq cm = 1 sq m; 35cm x 25cm = 875 sq cm) giving an answer of 11.

Love to know how she intends to make the 11th pane of glass from the leftover bits!

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 Post subject: Re: Maths Question - Teacher incorrect?Posted: Thu Nov 04, 2010 4:06 pm

Joined: Tue Jun 02, 2009 9:28 pm
Posts: 2439
The 11th pane is a broken pane! The question doesn't say anything about complete panes!

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 Post subject: Re: Maths Question - Teacher incorrect?Posted: Thu Nov 04, 2010 8:53 pm

Joined: Sun May 09, 2010 12:04 pm
Posts: 2609
wombat1 wrote:

I too came up with 10 - after drawing a diagram.

The teacher has told them to divide 10000 sq cm by 875 sq cm (10000 sq cm = 1 sq m; 35cm x 25cm = 875 sq cm) giving an answer of 11.

Love to know how she intends to make the 11th pane of glass from the leftover bits!

I am annoyed because I get also 11 and not 10 like you
I do it through a mathematical way, without drawing...
The area of the sheet of glass is: 100x 100 = 10 000 sq cm
The area of one pane of glass is: 35cm x 25cm = 875 sq cm

So I divided the area of the big sheet of glass by the area of one pane (long division, sorry, I can't find the horizontal line above the dividend and for the subtraction. How can I do that?):
11
___________
875 | 10000
-875
_____
1250
-875
_____
375

so that makes 11 panes of glass and there is a reminder...

Is it really important to work with a diagram and find 10? I am at a loss now?

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 Post subject: Re: Maths Question - Teacher incorrect?Posted: Thu Nov 04, 2010 8:54 pm

Joined: Sun May 09, 2010 12:04 pm
Posts: 2609
Oh gosh, when I sent my message, all the alignment of my division disappeared!!!

Well, you can do the division yourself on a piece of paper and understand what I meant

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 Post subject: Re: Maths Question - Teacher incorrect?Posted: Thu Nov 04, 2010 10:28 pm

Joined: Sat Feb 13, 2010 11:02 pm
Posts: 420
JaneEyre - why are you annoyed?

Isn't this one of those questions where you need to consider the rest of the info provided?

(a coach can carry 50 people, 75 students are going on a school trip, how many coaches are needed?
75/50=1.5, but the answer is 2)

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 Post subject: Re: Maths Question - Teacher incorrect?Posted: Thu Nov 04, 2010 10:36 pm

Joined: Fri Sep 15, 2006 8:51 am
Posts: 8115
JaneEyre wrote:
wombat1 wrote:

I too came up with 10 - after drawing a diagram.

The teacher has told them to divide 10000 sq cm by 875 sq cm (10000 sq cm = 1 sq m; 35cm x 25cm = 875 sq cm) giving an answer of 11.

Love to know how she intends to make the 11th pane of glass from the leftover bits!

I am annoyed because I get also 11 and not 10 like you
I do it through a mathematical way, without drawing...
The area of the sheet of glass is: 100x 100 = 10 000 sq cm
The area of one pane of glass is: 35cm x 25cm = 875 sq cm

So I divided the area of the big sheet of glass by the area of one pane (long division, sorry, I can't find the horizontal line above the dividend and for the subtraction. How can I do that?):
11
___________
875 | 10000
-875
_____
1250
-875
_____
375

so that makes 11 panes of glass and there is a reminder...

Is it really important to work with a diagram and find 10? I am at a loss now?

Trouble is your are trying to work out how many 875 sq cm shapes you can get regardless of their shape - the question has a specific shape mentioned. Bit like the crucial bus - you can't have a half a bus

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