# Slope of a budget constraint

Announcements Posted on
Why bother with a post grad? Are they even worth it? Have your say! 26-10-2016
1. The normal way i've been calculating slope is via 'the rise over the run' - i.e slope = changeinY/changeinX

for budget constraints, the textbook lists the slope as being

slope = -price of good X/price of good Y

in the one example I have, the two different calculations of the slope yield the same answer..soo i was wondering whether they always gave the same answer or whether this was just a concidence?

it also gives another formula,

changeinX = (changeinY x price of good Y)/ price of good X

i was wondering how this formula gave the change in X? is there some simple algebra behind it that proves it that i'm missing?

thanks
2. (Original post by redkopite)
The normal way i've been calculating slope is via 'the rise over the run' - i.e slope = changeinY/changeinX

for budget constraints, the textbook lists the slope as being

slope = -price of good X/price of good Y

in the one example I have, the two different calculations of the slope yield the same answer..soo i was wondering whether they always gave the same answer or whether this was just a concidence?

it also gives another formula,

changeinX = (changeinY x price of good Y)/ price of good X

i was wondering how this formula gave the change in X? is there some simple algebra behind it that proves it that i'm missing?

thanks
Should really post in the econ help forum, but anyhow... All of the above are the same thing...

change(X) = (change(Y)*Py)/Px
change(X)*Px = change(Y)*Py
change(Y)/change(X) = -Px/Py (you have to stick a minus in because budget constraints are downward sloping).

Take this example. You can work the budget eq as: y = -2x + 200, where Px=2 and Py=1. Slope = -Px/Py = -2, which is the same as dy/dx = -2

## Register

Thanks for posting! You just need to create an account in order to submit the post
1. this can't be left blank
2. this can't be left blank
3. this can't be left blank

6 characters or longer with both numbers and letters is safer

4. this can't be left empty
1. Oops, you need to agree to our Ts&Cs to register

Updated: April 7, 2009
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Today on TSR

### Who is getting a uni offer this half term?

Find out which unis are hot off the mark here

Poll
Useful resources