Year 7 maths problem

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secondtime
Posts: 138
Joined: Sat Apr 17, 2010 3:53 pm

Year 7 maths problem

Post by secondtime »

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? :evil:
aliportico
Posts: 888
Joined: Wed Aug 01, 2007 12:19 pm

Re: Year 7 maths problem

Post by aliportico »

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 :)
hermanmunster
Posts: 12818
Joined: Fri Sep 15, 2006 9:51 am
Location: The Seaside

Re: Year 7 maths problem

Post by hermanmunster »

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

Image
secondtime
Posts: 138
Joined: Sat Apr 17, 2010 3:53 pm

Re: Year 7 maths problem

Post by secondtime »

Thanks hermanmunster!

The teacher's explanation of 10000/600 was a little incorrect imho. However 16 is indeed right! :roll:
parent2013
Posts: 452
Joined: Mon Aug 12, 2013 10:13 am

Re: Year 7 maths problem

Post by parent2013 »

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 :)
ToadMum
Posts: 11947
Joined: Wed Jan 18, 2012 12:41 pm
Location: Essex

Re: Year 7 maths problem

Post by ToadMum »

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.
Outside of a dog, a book is a man's best friend. Inside of a dog it's too dark to read.Groucho Marx
Tinkers
Posts: 7240
Joined: Mon May 16, 2011 2:05 pm
Location: Reading

Re: Year 7 maths problem

Post by Tinkers »

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----
stevew61
Posts: 1786
Joined: Fri Nov 17, 2006 9:54 pm
Location: caversham

Re: Year 7 maths problem

Post by stevew61 »

The topic is tessellations, so it involves a bit of trial and error, and thinking rather than straightforward calculating.
Bobmumof3
Posts: 213
Joined: Sat Sep 14, 2013 8:15 pm

Re: Year 7 maths problem

Post by Bobmumof3 »

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?
Guest55
Posts: 16254
Joined: Mon Feb 12, 2007 2:21 pm

Re: Year 7 maths problem

Post by Guest55 »

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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