1. ## expression

I need to write this as an algebraic expression: During a drought a reservoir drops 3 in. ea. week for x straight weeks. Express the overall change in water level as an algebraic expression... Please and thank you!
I thought it would be -3n or -3(N) BUT MY PROF. TOOK HALF A POINT AWAY!

2. Originally Posted by thisflyispissinmeoff
I need to write this as an algebraic expression: During a drought a reservoir drops 3 in. ea. week for x straight weeks. Express the overall change in water level as an algebraic expression... Please and thank you!
I thought it would be -3n or -3(N) BUT MY PROF. TOOK HALF A POINT AWAY!
what is N?

you can't just state some variable and not say what it is

Let $N_0$ be the original level of the water before the drought.

Then, after $x$ weeks, the level of the water will be $N_0 - 3x$

3. Originally Posted by Jhevon
what is N?

you can't just state some variable and not say what it is

Let $N_0$ be the original level of the water before the drought.

Then, after $x$ weeks, the level of the water will be $N_0 - 3x$
i KNOW! tHIS WAS HIS EXACT QUESTION word FOR word stupid caps-sorry - I'm tired! I don't understand it at all, you need at least 1 more variable, right?

4. Originally Posted by Jhevon
what is N?

you can't just state some variable and not say what it is

Let $N_0$ be the original level of the water before the drought.

Then, after $x$ weeks, the level of the water will be $N_0 - 3x$
would it be (n-3)x ? u think? Thanks, by the way, for yor response!

5. Originally Posted by thisflyispissinmeoff
i KNOW! tHIS WAS HIS EXACT QUESTION word FOR word stupid caps-sorry - I'm tired! I don't understand it at all, you need at least 1 more variable, right?
well, it depends on how you want the answer to be expressed.

if you want to know the level of water after x weeks, then it is (N - 3x)

if you want to know by how many inches the water level dropped after x weeks, then it is 3x

6. Originally Posted by Jhevon
well, it depends on how you want the answer to be expressed.

if you want to know the level of water after x weeks, then it is (N - 3x)

if you want to know by how many inches the water level dropped after x weeks, then it is 3x
just 3x? what about the variable n? He wants "to express the overall change in water level 9AFTER 3 WKS) AS AN ALGEBRAIC EQUATION.

7. Originally Posted by thisflyispissinmeoff
just 3x? what about the variable n? He wants "to express the overall change in water level 9AFTER 3 WKS) AS AN ALGEBRAIC EQUATION.
ok, then it's just 3x, if you want an equation:

Let C be the change in the water level after x weeks

then, C = 3x

so after, say, 3 weeks, the change in the water level is 9 inches, since the water level will drop 9 inches over this period of time, which is what plugging in 3 into our formula yields