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PostPosted: Wed Mar 11, 2015 8:51 pm 
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Joined: Wed Mar 11, 2015 8:34 pm
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Please could someone help with this maths problem - ds really stuck!
The weights of 20 ear-rings were measured. Complete the table below so that the mean weight is 6.3g, the median weight is 6g and the modal weight is 7g.

weight of ear-ring 5g 6g 7g 8g
frequency 5 ? ? 2


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PostPosted: Wed Mar 11, 2015 9:04 pm 
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Joined: Mon Feb 12, 2007 1:21 pm
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Quote:
The weights of 20 ear-rings were measured. Complete the table below so that the mean weight is 6.3g, the median weight is 6g and the modal weight is 7g.

weight of ear-ring 5g 6g 7g 8g
frequency ..........5 ..? ...? ..2


The frequency has to add to 20 as there are 20 ear-rings.

Median is 6g so 10th and 11th have to be 6g

Modal is 7g so that frequency has to be highest.

Also mean is 6.3 - use that to check (5g x 5) + (6g x ? ) + (7g x ?) + (8g x 2) = 6.3 x 20

Try these hints


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PostPosted: Wed Mar 11, 2015 9:05 pm 
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there are 7 earrings accounted for so the 6g and 7g must =13

the commonest (modal) must be 7g and the median must be 6g

I tried splitting the 13 as 6*6g and 7*7g

then added up 5*5 + 6*6 + 7*7 + 2*8 = 126

126/20 gives 6.3g

maybe a better way then my guesswork but it seems to give the answer


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PostPosted: Wed Mar 11, 2015 9:26 pm 
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Thank you both - ds seems satisfied - he has worked the answers as 6 (for 6g) and 7 (for 7g).


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PostPosted: Wed Mar 11, 2015 9:31 pm 
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Yes - the mean is not needed other than to check as you can work the nubers out from knowing the median and the modal group.

Nice question ... might amend and borrow it!


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