Photoshop Contest Forum Index - General Discussion - MAth question...not PS stuff - Reply to topic
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blue_lurker
Location: Australia
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 Fri Feb 08, 2008 6:19 am Reply with quote
Ok Im sitting here helping my daugther to understand her math home work...not telling her how to do it but trying to help her understand...two questions stand out that had me puzzled
1. Chui-ting chose a CD and took it to the checkout desk. At the desk a 15% discount was given off the marked price because the CD was old stock. Then 10% gst was added. The final price was $22.44. What was the marked price.
ok thats the first one I tried to explain how to "reverse engineer the problem and well could not.
The second I don't understand hoping some one will explain it to me
2. By joining all the vertices of a decagon, how many diagonals are formed, what is the sum of all the angles of a decagon.
Never was very good at geometry so if you can help please do.
Oh and remember my daughter will be reading this with me so keep it PG13 please.
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dumbat
Location: Sydney
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Fri Feb 08, 2008 6:31 am Reply with quote
blue_lurker wrote: 1. Chui-ting chose a CD and took it to the checkout desk. At the desk a 15% discount was given off the marked price because the CD was old stock. Then 10% gst was added. The final price was $22.44. What was the marked price.
discounted price = 10/11 * 22.44 = 20.40
20.40 = 85% of marked price
orig price = 100/85 * 20.40 = 24.00
if it helps, here's another way to look at it
final = discounted + 10% ( = discounted * 1.1 )
22.44 = discounted * 1.1
discounted = 22.44 / 1.1
discounted = 20.4
discounted = orig - 15% ( = orig * 0.85 )
20.4 = orig * 0.85
orig = 20.4 / 0.85
orig = 24.00
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blue_lurker
Location: Australia
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Fri Feb 08, 2008 6:39 am Reply with quote
yep but Im trying to explain to her how its done not giving the answer, that's the part I'm having trouble with and she cant understand.
Its fine to have the answer but to explain how you got it is my problem
Thanks mate
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blue_lurker
Location: Australia
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Fri Feb 08, 2008 6:42 am Reply with quote
dumbat wrote: blue_lurker wrote: 1. Chui-ting chose a CD and took it to the checkout desk. At the desk a 15% discount was given off the marked price because the CD was old stock. Then 10% gst was added. The final price was $22.44. What was the marked price.
discounted price = 10/11 * 22.44 = 20.40
20.40 = 85% of marked price
orig price = 100/85 * 20.40 = 24.00
if it helps, here's another way to look at it
final = discounted + 10% ( = discounted * 1.1 )
22.44 = discounted * 1.1
discounted = 22.44 / 1.1
discounted = 20.4
discounted = orig - 15% ( = orig * 0.85 )
20.4 = orig * 0.85
orig = 20.4 / 0.85
orig = 24.00
ok but the gst is an added 10% whilst he 15% is a deduction.
so should you not need to know the discounted price first before you add the gst?
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dumbat
Location: Sydney
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Fri Feb 08, 2008 6:45 am Reply with quote
sorry 
well, you have to start at the end, with the final price, as that's the only absolute value you are given
the price was changed twice, in order to work from the final price to the marked price you have to reverse the 2nd change before the 1st
the 2nd change was to add 10% to a value, resulting in the final value. you can figure out the intermediate value from this
the 1st change was to take away 15% from the marked price to get this intermediate price
maybe it'd help to draw it in a simple flowchart?
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dumbat
Location: Sydney
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Fri Feb 08, 2008 6:48 am Reply with quote
blue_lurker wrote: you on msn mate? check your pm
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Lord David
Location: Melbourne, Australian Continent, Earth, Sector 001, United Federation of Planets, Alpha Quadrant.
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Fri Feb 08, 2008 7:27 am Reply with quote
dumbat wrote: blue_lurker wrote: 1. Chui-ting chose a CD and took it to the checkout desk. At the desk a 15% discount was given off the marked price because the CD was old stock. Then 10% gst was added. The final price was $22.44. What was the marked price.
discounted price = 10/11 * 22.44 = 20.40
20.40 = Get a calculator!
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dumbat
Location: Sydney
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Fri Feb 08, 2008 7:30 am Reply with quote
Lord David wrote: 20.40 = Get a calculator! ha ha, you think i did it in my head???   
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blue_lurker
Location: Australia
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Fri Feb 08, 2008 7:37 am Reply with quote
Lord David wrote: dumbat wrote: blue_lurker wrote: 1. Chui-ting chose a CD and took it to the checkout desk. At the desk a 15% discount was given off the marked price because the CD was old stock. Then 10% gst was added. The final price was $22.44. What was the marked price.
discounted price = 10/11 * 22.44 = 20.40
20.40 = Get a calculator!
that's great Dave but explain how you got those numbers to a 12 year old
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Tarmac
Location: Hotel California
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Fri Feb 08, 2008 7:55 am Reply with quote
blue_lurker wrote: Ok Im sitting here helping my daugther to understand her math home work...not telling her how to do it but trying to help her understand...two questions stand out that had me puzzled
2. By joining all the vertices of a decagon, how many diagonals are formed, what is the sum of all the angles of a decagon.
Never was very good at geometry so if you can help please do.
Oh and remember my daughter will be reading this with me so keep it PG13 please.
Blu, if she is anything like my own daughter, be prepared for tears with some sort of plea for relief or mercy near the end.
Here are two references that could help with your second question. Hopefully it won't befuddle things up even further. Either way, good luck to the both of you.
http://www.kjmaclean.com/Geometry/Decagon.html
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creatrix
Location: USA (but I didn't vote for the shrub.)
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Fri Feb 08, 2008 9:50 am Reply with quote
if x=original price,
22.44= (x * .85) *.90
Remeber, the 10% added is not 10% of the original price.
_________________
"Every cloud has a silver lining (except for the mushroom shaped ones, which have a lining of Iridium & Strontium 90)."
-Kevin Holmes
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creatrix
Location: USA (but I didn't vote for the shrub.)
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Fri Feb 08, 2008 9:51 am Reply with quote
Good god - are these 2 questions for the same class? One is 9th grade algebra and the other seems to be trig. Yikes. (I never took trig.... can't help ya there!)
_________________
"Every cloud has a silver lining (except for the mushroom shaped ones, which have a lining of Iridium & Strontium 90)."
-Kevin Holmes
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bigbuck
Location: Australia
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Fri Feb 08, 2008 10:01 am Reply with quote
sum of all the angles
a triangle (3 sided figure)has 180 degrees
A square (4 sided figure) is made of two triangles and has 360 degree
a pentagon has three triangles 3 x 180 degrees.
see the pattern?
3 sided fig has 1 tri
4 sided fig has 2
5 sided fig has 3
6 sided fig has 4
and so on....
So a decagon will have 8 triangles.
8 x 180 degrees
1440 degrees
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couldb5150
Location: California & Idaho
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Fri Feb 08, 2008 10:09 am Reply with quote
Tell her to forget it and not to worry for you have just deposited $6,00.00 in a bank account for her to get a boob job when she's 18 and a she'll never have any use in the real world for this math
anyhoo....her looks not intellect will get her all she needs employment wise!!!.....(OOPS DID I SAY THAT OUT LOUD?)
BWAHAHAHHHAHA
SORRY BLURKER MATH WAS NEVER MY STRONG AREA!!!!
~5150
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Photoshop Contest Forum Index - General Discussion - MAth question...not PS stuff - Reply to topic
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