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 Post subject: How would you explain this?Posted: Wed May 16, 2012 12:17 pm

Joined: Wed Mar 09, 2011 2:22 pm
Posts: 710
It's from the Heinemann 6 word problems book.

I am half-way halfway between 2 consecutive numbers. The product of the two numbers is 650.

I presume the two numers are 25 and 26 (by finding the square root of 650), making the 'half way' number 25.5?

How would you calculate this without a calculator though?

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 Post subject: Re: How would you explain this?Posted: Wed May 16, 2012 12:37 pm

Joined: Sat Oct 09, 2010 10:46 am
Posts: 182
You could factorise and combine I.e 650= 10*65 =5*2*5*13 =5*5*13*2 = 25*26

Sgcmum

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 Post subject: Re: How would you explain this?Posted: Wed May 16, 2012 2:12 pm

Joined: Mon Aug 22, 2011 12:12 pm
Posts: 366
I like sgcmum's method alot. Another way I use is think in 10's. 20x20=400, 30x30=900, its between there. Go half way i.e. 25x25=625 (closer but still lower), 26x26=676 (closer but now higher) so that's it gotta be 25 and 26.

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 Post subject: Re: How would you explain this?Posted: Thu May 17, 2012 8:26 pm

Joined: Tue Jul 21, 2009 9:56 pm
Posts: 8228
Or you'd solve a quadratic equation?

x ( x +1 ) = 650

x2 + x -650 = 0

Then solve as usual.

The answer would be halfway between x and x+1. Would quadratic equations be expected for this particular Heinemann paper?

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 Post subject: Re: How would you explain this?Posted: Thu May 17, 2012 8:28 pm

Joined: Tue Jul 21, 2009 9:56 pm
Posts: 8228
oops sorry that would need a calculator too. Does it need to be done without a calculator? If so, the other methods win.

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 Post subject: Re: How would you explain this?Posted: Thu May 17, 2012 9:09 pm

Joined: Mon Jun 18, 2007 2:32 pm
Posts: 6966
Location: East Kent
I wouldn't expect quadratic equations for yr 6

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 Post subject: Re: How would you explain this?Posted: Thu May 17, 2012 9:52 pm

Joined: Thu May 10, 2012 8:30 am
Posts: 247
Manana wrote:
It's from the Heinemann 6 word problems book.

I am half-way halfway between 2 consecutive numbers. The product of the two numbers is 650.

I presume the two numers are 25 and 26 (by finding the square root of 650), making the 'half way' number 25.5?

How would you calculate this without a calculator though?

I wonder if -25.5 would be marked correct?

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