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10 April, 10:34

There are 25 desks in a classroom. The number of rows is five less than twice the number of desks in each row. Find the number of rows and the number of desks in each row.

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  1. 10 April, 10:40
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    Let's say each row has x desks and there are y rows.

    We then know that x*y = 25

    We also know that x*2-5=y (number number of rows is five less than twice the number of desks in each row)

    So we substitute: x * (x*2-5) = 25

    putting numbers out of the brackets:

    2x*x-5x=25

    2x*x-5x-25=0

    (2x+5) (x-5) = 0 (this bracketing is true: you can check it by expanding it:

    2x*x-10x+5x-25

    So that means that either x=-2.5which can't be : there can't be a fractional number of benches,

    or x=5

    so each row has 5 desks and there are 2*5-5 rows, or 5 rows.
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