# The amount of chlorine in a pool today is 5/18 the amount of chlorine in the pool yesterday. By what fraction did the amount of chlorine decrease? To find the fraction by which the amount of chlorine decreased:

Let x be the amount of chlorine in the pool yesterday.

The amount of chlorine in the pool today is `5/18` of x, or `5/18*(x)`

The amount of decrease = amount of chlorine yesterday - amount of chlorine...

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To find the fraction by which the amount of chlorine decreased:

Let x be the amount of chlorine in the pool yesterday.

The amount of chlorine in the pool today is `5/18` of x, or `5/18*(x)`

The amount of decrease = amount of chlorine yesterday - amount of chlorine today.

`x- 5/18 x`

By making the denominators the same and subtracting, we get

`(18x-5x)/18` `rArr (13x)/18`

which can be written as `(13/18) x` and means `13/18` of x.

The quantity x has been decreased to `5/18` of x by subtracting `13/18` of x.

So the fraction by which the amount of chlorine decreased is `13/18` .

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