ferterliser in paddock problem

**vegito12** · August 11th 2010, 08:41 PM

A farmer needs to spread fertiliser over a paddock measuring 40 m by 80 m. The instructions on the fertiliser bag say to use 80 grams per square metre. How many kilograms of fertiliser will be needed?

I did 80 divied by 1000 = 0.08 kg is that right?

**eumyang** · August 11th 2010, 09:09 PM

All you did was convert 80 g to kg. But 0.08 kg of fertilizer is supposed to be used for 1 square meter. But the paddock is not 1 square meter, is it? How do we find out the area of this paddock?

**vegito12** · August 11th 2010, 09:17 PM

would it be 40m x 80m = 3200/ 1000 = 3.2 kg

**eumyang** · August 11th 2010, 09:32 PM

No, that's not right. You got the area, $3200\,\text{m}^2$ . Why on earth would you try to convert to kg by dividing by 1000? Can't do that, my friend.

We have a proportion here. If 0.08 kg is used for $1\,\text{m}^2$ , how many kilograms is used for $3200\,\text{m}^2$ ? You could set up the proportion like this:
$\dfrac{0.08}{1} = \dfrac{x}{3200}$
... and solve for x.

**vegito12** · August 11th 2010, 09:32 PM

would 0.08 x 3200 = 256 kg for 3200 be correct

**eumyang** · August 11th 2010, 09:34 PM

Yes, it is 256 kg.

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