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emma51 · Nov 10, 2009, 02:13 AM

please could someone help me answer this question??

y= 900a /
2 + a

Unknown008 · Nov 10, 2009, 03:24 AM

Do you want to make 'a' the subject of formula?

emma51 · Nov 10, 2009, 04:19 AM

Yes

Unknown008 · Nov 10, 2009, 04:21 AM

Ok, I'll tell you to multiply each side by a+2 first and let's see what you get.

I'll be guiding you till the answer. :)

emma51 · Nov 10, 2009, 05:35 AM

THIS IS WHAT I GOT

2y + ay +900a
2y + 900a - ay
2y= (900-y)a
a= 2y/900-y

= 2y/900-2y/y
= y/450-2

this is the answer I got

Perito · Nov 10, 2009, 05:59 AM

2y + ay = 900a

2y = 900a - ay

Watch your "=" signs.

2y= (900-y)a

$a= \frac {2y}{(900-y)}$

So far, so good. "a" is now the subject of the expression.

This is wrong. You can't simply put the numerator over each element of the denominator.

$a \ne 2y/900-2y/y$

$a \ne y/450-2$

You could do this:

$a=\frac {\left( \frac {2y}{2} \right) }{\left( \frac {900-y}{2} \right)} = \frac {y}{\left( \frac {900}{2} - \frac {y}{2} \right)$

$a = \frac {y}{450-y/2}$

but I'm not sure why you'd want to do that.

Unknown008 · Nov 10, 2009, 06:51 AM

Yes, leave it as $a = \frac{2y}{900-y}$ that's fine.

emma51 · Nov 11, 2009, 02:12 AM

I did the equation like that as the question was:

A major chemical company researching crop yields tries out a new pesticide. The results indicate that, per hectare, for a kg of pesticide the extra yield y kg of a crop is given by the equation

the question was:

what is the formula which gives the amount, a kg, of pesticide needed to return and extra yield of y kg?

Unknown008 · Nov 11, 2009, 03:04 AM

Yes, you leave it as said previously. :)

emma51 · Nov 11, 2009, 04:53 AM

Thanks for your help :)

Unknown008 · Nov 11, 2009, 06:14 AM

You're welcome! :)