<p>Yes, typically we would like estimate these curves’ functional forms. If we estimate a demand function <span class="math-container">$P=10-2Q$</span> we can rearrange it such that <span class="math-container">$Q=5-\frac{1}{2}P$</span>. </p>

<p>This, just changes the way we interpret the relationship. For a given quantity how does price change? Compared to, for a given price how does quantity change? This begs even further questions however because in the market we typically just observe equilibriums and “shocks” that determine prices typically also affect quantity. This makes estimating these functional forms difficult from an econometrics point of view.</p>

CC BY-SA 4.0
2019-10-09T09:06:54.377Z
Actually the demand function is $Q(P)$. The *inverse demand function* is $P(Q)$. See more [here](https://en.wikipedia.org/wiki/Inverse_demand_function).
Art
CC BY-SA 4.0
2019-10-09T16:47:47.377Z
Yes I should have used my language more properly here, thank you
Brennan
CC BY-SA 4.0
2019-10-09T17:10:53.247Z
Thank you for a reply , I saw a gold graph once and the price was changing according to time not the quantity. And people start to draw as they call it trend lines (upward and downward ) so if the trend is up they call it Supply if the trend is down it is a demand graph, is this right ?  Is there way to find the quantity of gold that traded in this example?.
user3741124
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2019-10-09T22:37:36.590Z
If you edit your question to include what you are talking about I would more than gladly update my answer to see if I can answer!
Brennan
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2019-10-10T09:20:38.913Z
I just updated my question. Thank you very much
user3741124
CC BY-SA 4.0
2019-10-08T15:02:35.337Z
2019-10-08T15:02:35.337Z
Brennan
<p>i have some basic knowledge on economics ,and i had an argument with a friend ,so  my question is this , as we all know 
(If we ignore all the outside factors) that the price of any product is governed by it's quantity in the market. So the more from that product existing in the market the lower the prices and vise versa. 
Is there a method or formula that works backwards i mean from the price of that product you can find the quantity that represented in the market ??</p>

<p><strong>Update:</strong> 
I saw a gold graph once and the price was changing according to time not the quantity. And people start to draw as they call it trend lines (upward and downward ) so if the trend is up they call it Supply if the trend is down it is a demand graph, is this right ? Is there  a way to find the quantity of gold that traded in this example from the graph it self ? Of course we still ignoring the other factors that could change market direction we talk only supply and demand.
Maybe it is a silly question .... sorry.
<img src="https://i.sstatic.net/Rc5dN.png" alt="enter image description here"></p>

<supply-and-demand>
A basic question about supply and demand graph
user3741124
# A basic question about supply and demand graph

(Asked by: username_0 on 2019-10-08)

i have some basic knowledge on economics ,and i had an argument with a friend ,so my question is this , as we all know
(If we ignore all the outside factors) that the price of any product is governed by it's quantity in the market. So the more from that product existing in the market the lower the prices and vise versa.
Is there a method or formula that works backwards i mean from the price of that product you can find the quantity that represented in the market ??

**Update:**
I saw a gold graph once and the price was changing according to time not the quantity. And people start to draw as they call it trend lines (upward and downward ) so if the trend is up they call it Supply if the trend is down it is a demand graph, is this right ? Is there a way to find the quantity of gold that traded in this example from the graph it self ? Of course we still ignoring the other factors that could change market direction we talk only supply and demand.
Maybe it is a silly question .... sorry.
![enter image description here](https://i.sstatic.net/Rc5dN.png)

**Tags:** supply-and-demand


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## 1 answers

### Answer by username_1 on 2019-10-08. Score: 3

Yes, typically we would like estimate these curves’ functional forms. If we estimate a demand function $P=10-2Q$ we can rearrange it such that $Q=5-\frac{1}{2}P$.

This, just changes the way we interpret the relationship. For a given quantity how does price change? Compared to, for a given price how does quantity change? This begs even further questions however because in the market we typically just observe equilibriums and “shocks” that determine prices typically also affect quantity. This makes estimating these functional forms difficult from an econometrics point of view.

> **Comments:**
> **username_2**: Actually the demand function is $Q(P)$. The *inverse demand function* is $P(Q)$. See more [here](https://en.wikipedia.org/wiki/Inverse_demand_function).  
> **username_1**: Yes I should have used my language more properly here, thank you  
> **username_0**: Thank you for a reply , I saw a gold graph once and the price was changing according to time not the quantity. And people start to draw as they call it trend lines (upward and downward ) so if the trend is up they call it Supply if the trend is down it is a demand graph, is this right ?  Is there way to find the quantity of gold that traded in this example?.  
> **username_1**: If you edit your question to include what you are talking about I would more than gladly update my answer to see if I can answer!  
> **username_0**: I just updated my question. Thank you very much  

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