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1 March, 12:55

Mary needs to send out some letters and postcards. She went online at the United States Postal Service webpage and found out that it cost 45 cents to mail a letter and 35 cents to mail a postcard. Mary wrote to 15 people and the cost of postage was $6.15. If it cost 35 cents to mail a postcard and 49 cents to mail a letter, how many letters and how many postcards did he send?

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  1. 1 March, 13:08
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    Answer:6 postcards and 9 letters

    Step-by-step explanation:

    First we label what we are looking for

    Label number of postcard sent as x

    Label number of letter sent as y

    The we know Mary wrote to 15people, either as postcard or letter, so from this we make an equation

    x + y = 15 (1)

    The we know the amount Mary used to send all this is $6.15 which is also 615 cents

    Then we know sending one postcard is 35cents, and we labeled number of postcards to be x

    So total amount used for postcard will be 35x

    And we know sending one letter is 45 cents, and we labeled number of letters to be y

    So total amount used for letter will be 45y, so adding all this will be equals to the total amount used which is given as $6.15 also 615 cents, so making another equation

    35x + 45y = 615 (2)

    Solving the two simultaneously equations

    x + y = 15 (1)

    35x + 45y = 615 (2)

    So we make y the subject of formula in (1)

    y = 15 - x (3)

    So we put (3) in (2)

    Anywhere we see y, we put 15-x

    35x + 45 (15-x) = 615

    35x + 675 - 45x = 615

    35x - 45x = 615 - 675

    -10x = - 60

    divide both sides by - 10

    x = 6

    So therefore, number of postcards is 6

    Then we put x = 6 in (3)

    y = 15 - x

    y = 15 - 6

    y = 9

    So therefore number of letters is 9
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