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PostPosted: Tue Oct 19, 2010 9:55 pm 
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Joined: Mon Apr 28, 2008 9:57 am
Posts: 223
Can someone please help with the sum below, dS is demanding a mark for the question as he thinks there are two answers to it. :roll:


(15[32]2 ) (14[30]2)
(12[?]4)

Answer is 28 but ds thinks it can also be 26
Is there a technique to working out the correct answer?

Thank you


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PostPosted: Tue Oct 19, 2010 10:03 pm 
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Quote:
(15[32]2 ) (14[30]2)
(12[?]4)

(15x2)+2=32
(14x2)+2=30
(12x2)+4=28
How does your ds get to 26?

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PostPosted: Tue Oct 19, 2010 10:22 pm 
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Hi turtleglos

DS thought he should be adding 2 each time instead of the number on the right.

Many thanks


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PostPosted: Wed Oct 20, 2010 12:17 pm 
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Location: Essex
Couldn't it also be 52? Product of the two outside numbers plus the number to the right.


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PostPosted: Wed Oct 20, 2010 12:35 pm 
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Quote:
Couldn't it also be 52? Product of the two outside numbers plus the number to the right.
Couldn't it also be 52? Product of the two outside numbers plus the number to the right.

It could, but I would guess that that is not an option in the multiple choice.

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PostPosted: Wed Oct 20, 2010 1:50 pm 
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Hi Josa. The instructions for this type of question in the SD papers state that "The three numbers in each group are related in the same way". I believe that your son's alternative answer does not use one of the numbers in the group for the final group? I would say his answer is therefore incorrect. It is my understanding that you must include both numbers outside the brackets for these types of questions.

As an aside however, when I first looked this up I used the Tutors papers as an example, and their instructions are "In these questions, the middle number in the last group is made up in the same way as the middle number in the first two groups". In this case I would argue that your son's answer would be allowable - but it is not the standard approach and I would not encourage it.


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PostPosted: Wed Oct 20, 2010 5:45 pm 
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hi turtleglos,
dd chose 28 as the answer when she was doing it as a multiple choice paper but gave 52 as the answer when i gave it as part of a standard test!

sgcmum.


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PostPosted: Wed Oct 20, 2010 5:49 pm 
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52 was my first thought too, but 28 is equally valid.
26 cannot work as the 4 has not been used from the second set, but a totally reasonable error.


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PostPosted: Wed Oct 27, 2010 4:51 pm 
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15[32]2 ) (14[30]2)
(12[?]4)

There are three credible answers to this question. Fortunately only one of the answers appears on the answer sheet. This question therefore should never be used in standard format.

15 x 2 = 30
30 plus 2 = 32

14 x 2 = 28
28 plus 2 = 30

12 x 4 = 48
48 plus 2 = 50

or:

15 plus 2 =17
17 plus the number on the left = 32

14 plus 2 = 16
16 plus the number on the left = 30

12 plus 4 = 16
16 plus the number on the left = 28

or

15 x 2 = 30
30 plus the number on the right = 32

14 x 2 = 28
28 plus the number on the right = 30

12 x 4 = 48
48 plus the number on the right = 52


Patricia


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