00:01
In this problem, the demand function of the product is modeled by p equals to 400 minus 4x and where x is between 0 to 100, right? so where p is the price per unit in dollars and x is the number of units.
00:23
Okay, so first of all from this given demand function for a product, right? so we will just write in terms of x what will be the value.
00:35
So x will be equals to what? this will be equals to 400 minus p upon 4.
00:50
So why i am doing this? i'll let you know afterwards.
00:53
You will get to know that why i am doing this.
00:55
So this is basically you can say that this is the value of x.
00:59
So now here it is as that determine when the demand is elastic and inelastic.
01:07
So, elastic demand, first of all, let us write here a, this is first, elastic demand, e is given by minus p by x into dx by dp.
01:35
Right? so this is equation number one.
01:37
So now you got to know that why i'm doing this.
01:41
Okay.
01:41
So this is the basic formula for the elastic demand.
01:45
Okay so you must remember this now you can find out you can just differentiate this equation what we have found for x so here d x by d p will be equal to we will just differentiate it we will be getting 1 by 4 this is differentiation of 400 will be 0 right and differentiation of p will be equals to 0 again right so this means that i'm sorry this is differentiation of p will be equal to minus 1 here right so this becomes d x by d p equals to minus 1 by 4 right so now we will just put this value so therefore equation 1 becomes e equals to minus p by x multiplied with minus 1 by 4 which is equal to p by 4x right okay now here e will be equal to 400 minus 4x by 4x which is equal to 4 into 100 minus 4 x by 4x which is equal to 4 into 100 minus divided by 4 which is equals to 100 minus 2 by x here.
04:10
So this should be not 4, this should be x, okay? so here this cuts off right.
04:20
So now the demand is elastic when...