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PostPosted: Sun Jan 11, 2015 12:56 pm 
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question is about various numbers of discs (D), envelopes (E) and squares (S) in balance, they show pictures of scales which are in balance, so ...

A) 2D + 1E = 2S
2D + 3E = 3S

4D + 3E = ?

The top two are in perfect balance. How many squares are needed to balance the bottom set (what is ?).

I MAKE THE ANSWER 5 squares (because 2D + 2D = 4D and 1E + 3E = 4E, therefore 2S + 3S = 5s)

B) [the shapes may not weigh the same as in part (a)]

5D + 1E = 5S

3D + 2E = 4S

6E = ?

The top two scales are in perfect balance. How many squares will be needed to balance the bottom set?



NO IDEA HOW TO WORK THIS OUT!!

...Thank you


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PostPosted: Sun Jan 11, 2015 1:12 pm 
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For a), is there an error in your second equation?

For b), your starting point could be 5D + 1E = 5S, so

10D + 2E = 10S

nyr


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PostPosted: Sun Jan 11, 2015 1:29 pm 
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nyr - isn't it better to elimiate E as we're not interested in it?


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PostPosted: Sun Jan 11, 2015 1:40 pm 
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Sorry yes error - part a last equation should say 4D + 4E = ?

None the wiser with part B


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PostPosted: Sun Jan 11, 2015 1:48 pm 
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5D + 1E = 5S

3D + 2E = 4S

6E = ?

How could you get the same numbers of Ds in each equation - try this and then get back to me. If I just post the whole solution it won't help you with the next one.


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PostPosted: Sun Jan 11, 2015 2:10 pm 
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I'm getting an answer of 6 squares.. Is that right?


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PostPosted: Sun Jan 11, 2015 2:32 pm 
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Can you post or PM me your working ? Also double check the original equations as I seem to be getting fractions :shock:


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PostPosted: Sun Jan 11, 2015 3:12 pm 
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AML wrote:
B) [the shapes may not weigh the same as in part (a)]

5D + 1E = 5S

3D + 2E = 4S

6E = ?

The top two scales are in perfect balance. How many squares will be needed to balance the bottom set?


Multiply the 1st equation by 3: 15D + 3E = 15S
Multiply the 2nd equation by 5: 15D + 10E = 20S

Subtract these and the D bit will disappear.

7E=5S

Hmmm. 6E = 5S *6/7

Are you sure you haven't got another typo when you've given us the question?


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PostPosted: Sun Jan 11, 2015 3:22 pm 
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DebsB - it's better to give a hint rather than a full solution ... yes I hit the same issue, hence my post.


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PostPosted: Sun Jan 11, 2015 3:38 pm 
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arghhh, definitely another typo.

Apologies!

So last line should be 7E ..... (not 6E)


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