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 Post subject: Year 7 maths problemPosted: Thu Mar 13, 2014 11:41 am

Joined: Sat Apr 17, 2010 2:53 pm
Posts: 138
Question:

How many panes of glass 30cmx20cm can be cut from a sheet which is 1 metre square?

DD worked out answer to be 15.

Answer corrected by teacher to 16. I don't understand correction. I get 15 too as surely they need to be whole sheets?
What am I missing?

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 Post subject: Re: Year 7 maths problemPosted: Thu Mar 13, 2014 11:47 am

Joined: Wed Aug 01, 2007 11:19 am
Posts: 888
Your dd is right! Teacher perhaps has just done 10000/600? If it is definitely 1 metre square, and not 1 square metre, to be arranged in whatever the optimum rectangle would be.

Your dd should just ask the teacher to draw it for her

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 Post subject: Re: Year 7 maths problemPosted: Thu Mar 13, 2014 11:49 am

Joined: Fri Sep 15, 2006 8:51 am
Posts: 8113
hmm is it one of these ones where you can get 2*30cm + 2*20cm on one side ?

so one quarter of the sheet = 50cm by 50cm and you could get 4 pieces arranged with a 20 and a 30 on each side in a pattern like this picture : (well each quarter of your sheet would be one of these small squares on this) and there would be a little bit in the middle left over

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 Post subject: Re: Year 7 maths problemPosted: Thu Mar 13, 2014 12:01 pm

Joined: Sat Apr 17, 2010 2:53 pm
Posts: 138
Thanks hermanmunster!

The teacher's explanation of 10000/600 was a little incorrect imho. However 16 is indeed right!

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 Post subject: Re: Year 7 maths problemPosted: Thu Mar 13, 2014 5:07 pm

Joined: Mon Aug 12, 2013 9:13 am
Posts: 452
15 panes, unless the teacher wants to cut the 16th one into smaller pieces and fit in the remainder 10x100 cm area.

Not surprised by the teaching standard, I guess parents are more intelligent these days. God help the class

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 Post subject: Re: Year 7 maths problemPosted: Thu Mar 13, 2014 5:25 pm

Joined: Wed Jan 18, 2012 11:41 am
Posts: 4587
Location: Essex
Having no luck trying to draw this out in Word, but try:

4 columns - two of one pane across, 5 down (landscape) and two of one pane across, three down (portrait). There will be a 10cm x 40cm piece of glass remaining at the base of the third and fourth columns.

16 panes total.

_________________
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 Post subject: Re: Year 7 maths problemPosted: Thu Mar 13, 2014 5:39 pm

Joined: Mon May 16, 2011 1:05 pm
Posts: 4019
I've drawn it out and got 16 too. Drawn differently to Herman.
Hopefully this helps. Letters grouped together signify a pane of glass.

oooxxxooxx
oooxxxooxx
xxxcccooxx
xxxcccxxoo
ccceeexxoo
ccceeexxoo
eeeaaaooxx
eeeaaaooxx
ccceeeooxx
ccceee----

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 Post subject: Re: Year 7 maths problemPosted: Thu Mar 13, 2014 5:51 pm

Joined: Fri Nov 17, 2006 8:54 pm
Posts: 1770
Location: caversham
The topic is tessellations, so it involves a bit of trial and error, and thinking rather than straightforward calculating.

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 Post subject: Re: Year 7 maths problemPosted: Thu Mar 13, 2014 7:00 pm

Joined: Sat Sep 14, 2013 7:15 pm
Posts: 213
Why is 10000/600 wrong? That's how I would have worked it out?

Area 100x100= 10000

Area of tile 20x30=600

So 10000/600 = 16.67. So 16 complete tiles?

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 Post subject: Re: Year 7 maths problemPosted: Thu Mar 13, 2014 7:11 pm

Joined: Mon Feb 12, 2007 1:21 pm
Posts: 11936
That method assumes the shapes fit in with nothing to spare.

These questions always need you to look at whether dimensions fit; it is not really about area.

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