Math

400 exercise books are arranged into 3 piles.The first has 5 more books than the 2nd pile.The number of books in the second pile is twice the number of books in the third pile.How many books are there in the third pile??

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  1. P1 = first pile

    P3 = second pile

    P3 = third pile

    The first has 5 more books than the 2nd pile.

    This mean :

    P1 = P2 + 5

    The number of books in the second pile is twice the number of books in the third pile.

    This mean :

    P2 = 2 P3

    So if :

    P2 = 2 P3 and P1 = P2 + 5 then :

    P1 = P2 + 5

    P1 = 2 P3 + 5

    Total number of books = 400

    P1 + P2 + P3 = 400

    2 P3 + 5 + 2 P3 + P3 = 400

    5 P3 + 5 = 400 Subtract 5 to both sides

    5 P3 + 5 - 5 = 400 - 5

    5 P3 = 395 Divide both sides by 5

    5 P3 / 5 = 395 / 5

    P3 = 79

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  2. P2 = second pile

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  3. Paul, if you had looked back, you would have seen that variations of your question have been answered several times

    I even did it for you both ways, with 300 books and with 3000 books.

    ignore Oscar's reply, I have shown it to be wrong

    http://www.jiskha.com/display.cgi?id=1450819688

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