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Melody

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यूजर का नामMelody
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Melody  11 Feb 2022
 #1
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Vraces:

*Need serious help

In a crack smoking neighborhood the people have been over 20 years reduced to half of what they originally were. What yearly reducing in percent is this?

[I already have the answer, but I can't figure out w*f to do to solve it(I'm getting the wrong answer) cause I'm an idiot]
If you don't think you can solve it don't write s**t that'll confuse me further, I'm confused enough as it is.


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Hi Vraces,
I sent you 2 private messages way back at the beginning of Dec, I know that you haven't read them because they are still sitting in my outbox
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Now for your problem, (this is lead up to your problem)
Just say that there were 1000 rabbits in a field and the population is decreasing by an average of 5% each year. 5% as a decimal is 0.05
so, at the end of each year there would be (100%-5%=95%) which is (1-0.05) of the early January population.
So at the end of the first year there would be 1000*(1-0.05)
At the end of the second year there would be 1000*(1-0.05) (1-0.05) = 1000*(1-0.05) 2 [this is the number of rabbits at the beginning of the second year * (1-0.05)]
.....
At the end of the 20th year there would be about 1000*(1-0.05) 20 rabbits.

Are you with me so far?
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Now lets look at your problem
In the beginning there were P crack users.
After 20 years there were P/2 crack users. (P/2 is the same as 0.5P)
Let the average yearly reduction rate be r (not r%, this is a decimal, so if it was 5%, r=0.05)

We have

P/2 = P(1-r) 20
0.5P = P(1-r) 20
divide both sides by P
0.5 = (1-r) 20
Raise both sidesby the power of 1/20
0.5^(1/20) = 1-r
r = 1 - 0.5^(1/20)
r = 0.034 (correct to 3 dp)
so the number of crack users is reducing by a average yearly rate of 3.4%
Is this answer the same as the one given?
do you understand?

PS You are not an idiot and a little less bad language on the forum would be good.
17 Jan 2014
 #1
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guest:

Dear All,

Please help to check my answer for below questions :

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the demand function of a product is : Q = 500 - 40P + P2

P : price/unit (dollar), and Q : the amount of production.

questions :

a. Determine the elasticity of demand when the price is = 15.
b. If the price is increased by 5%, what will happen to the demand?

my answer :

a. Q = 500 - (40x15) + 152
= 500 - 600 + 225
= 125

if Q = 500 - 40P + P2, then Q1 = 2P - 40, and P1 = - 1/40 + 1/P
if Q = 500 - 40P + P2, then dQ/dP = 2P - 40, and where did you get P' from?
So I guess Q'=2*15-40=-10

E = dQ/dP x P/Q
= -10 x 15/125
= -1,2 (Do you use commas instead of decimal points?)

b. If the price is increased by 5%, the demand will be decrease to = 1,2 x 5 = 6 (I don't think so)

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Thank you very much for the correction..


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I have never done this before, I just googled it then to see if I could help you.
I think that part a is correct except for the coloured changes/ additions that I did.

Now part b
E = -1.2
I think this means that if price goes up by 1.2%, the demand will go down by 1%
You want to know what will happen to demand if the price goes up by 5%
so let the change in demand be d%
so this is the equation that you have to solve.
1.2% / 1% = 5% / d%

1.2 = 5/d
d = 5/1.2
d = 4.2 (1 dec places)

so if the price increases by 5% I think that the demand will decrease by 4.2%

Like I said, I hadn't even heard these terms before I googled them for you just a moment ago.
But that's what I think.
17 Jan 2014