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Math Help - 1200 stamps problem (with suggested solution)

  1. #1
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    1200 stamps problem (with suggested solution)

    There is a collection of stamps where 68% are foreign stamps, 45% are issued more than 10 years ago and 30% are foreign stamps issued over 10 year ago.
    There are 1200 stamps in total.

    How many foreign stamps issued within 10 years?

    My solution is (look at the image below):

    Attachment 19830

    68% of 1200 = 816 which is the total number of Foreign stamps
    45% of 1200 = 540 which is the total of 10+ stamps. Therefore 660 are total of foreign stamps issued 10- years.
    30% of 660 = 198 which is the foreign stamps issued 10- years.

    The answer is : 198

    Thank you in advance
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  2. #2
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    You are given that "45% of the stamps were issued more than 10 years ago". You are assuming that that same percentage applies to both domestic and foreign stamps. What right do you have to make that assumption?
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  3. #3
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    I can't solve better than that. any suggestion? so you're saying that the question is incomplete or what?
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  4. #4
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    Hello, Narek!

    Exactly where is your difficulty?


    There is a collection of 1200 stamps.
    68% are foreign stamps.
    45% are issued more than 10 years ago . (This is irrelevant.)
    and 30% are foreign stamps issued over 10 year ago ("old").

    How many foreign stamps issued within 10 years ("new")?

    There are: . 68\% \times 1200 \:=\:816 foreign stamps.

    There are: . 30\% \times 1200 \:=\:360 foreign stamps which are old.

    Therefore, there are: . 816 - 360 \:=\:456 foreign stamps which are new.

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  5. #5
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    no, I don't think this is correct. 45% of all the stamps are issued more thant 10 years ago. Therefore, 55% are issued within 10 years.
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  6. #6
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    Hello, Narek!

    There is a collection of 1200 stamps.
    68% are foreign stamps,
    45% are issued more than 10 years ago ("old")
    30% are foreign stamps issued over 10 year ago.

    How many foreign stamps issued within 10 years ("new")?

    Place the information in a chart . . .

    . . \begin{array}{c||c|c||c|}<br />
& \text{Old} & \text{New} & \text{Total} \\ \hline\hline<br />
\text{Foreign} & {\bf30\%} & & {\bf68\%} \\ \hline<br />
\text{U.S.} & & & &  \hline\hline<br />
\text{Total} & {\bf45\%} & & 100\% \\ \hline \end{array}


    Complete the chart:

    . . \begin{array}{c||c|c||c|}<br />
& \text{Old} & \text{New} & \text{Total} \\ \hline\hline<br />
\text{Foreign} & 30\% & {\bf38\%} & 68\% \\ \hline<br />
\text{U.S.} & {\bf15\%} & {\bf17\%} & {\bf32\%} \\  \hline\hline<br />
\text{Total} & 45\% & {\bf55\%} & 100\% \\ \hline \end{array}


    The question is "How many stamps are foreign and new?"

    Answer: . \text{38\% of 1200}

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  7. #7
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    Code:
            Number     > 10 years
    Foreign 816 (68%)  244.8 (30% of 816)
    Local   384 (32%)  295.2 (540 - 244.8)
           ====        =====
    Total  1200        540.0 (45% of 1200)
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  8. #8
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    Thank you folks for the answers but as you see we have 3 different answers here! 3 different approaches, excluding mine! Which one do you think is the correct answer?
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  9. #9
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    Quote Originally Posted by Narek View Post
    Thank you folks for the answers but as you see we have 3 different answers here! 3 different approaches, excluding mine! Which one do you think is the correct answer?
    Well, show all 4 solutions to your teacher: it'll prove how unclear he/she is!!

    For the record: I'm sure that Soroban's answer of 456 is what's intended.

    There are 816 (1200 * .62) F-stamps
    There are 360 (1200 * .30) F-stamps > 10y
    There are 456 (816 - 360) F-stamps =< 10y

    Problem should be clarified, like:
    A collection contains 1200 stamps.
    68% of the collection are Foreign stamps.
    30% of the collection are Foreign stamps > 10 years.
    How many Foreign stamps are =< 10 years ?
    Last edited by Wilmer; November 25th 2010 at 08:45 AM.
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