# Question 28b (i) + (ii)- The Mexican Q (1 Viewer)

#### nikki_ice

##### New Member
Hey guys....I know this question was really weird, but Im just having a go at giving you some possible answers to this...I dont know if it was right, but it gave me an answer that looked reasonable.

b)
Given:
(i) growth rate = 1.57% / annum, y = estimated number of ppl in Mexico at a time x years after 2002. Write the formula relating x and y in form y=b(a^x)

So we had to write a formula including appropriate values for a and b in the formula.

I thought of using the compound interest formula A = P(1+r)^n, as it requires similar calculations and asks similar things, for eg. accumulation, or 'compounding' of years.

so I said : y = a ( 1 + b ) ^ x , where y = estimated number of ppl in Mexico at a time x years after 2002, a= initial population, b = growth rate, x = compounding periods.

but i wasn't sure if it should be y=P(1+r)^x

(ii) using formula y=a(1+b)^x,
y = 103 400 000 x (1 + 1.57/100 ) ^ 2

y = 106, 627, 247 (to nearest thousand)

I had a go at least! You get marks for having a go, even if you only lose one for getting the wrong result. Hope y ll can understand that!

Im outtie!

#### Lundy

##### Banned
You definitely had a better go at it than I did

#### honky tonk

##### in Miracle World
Originally posted by nikki_ice
y = 106, 627, 247
Yeah, I got the same answer.. whether it's right is another story.

#### parko

##### RN in 2007
i think i had something along those lines..........i dunno i didnt write my working in my question booklet, just straight onto the page for that one and now i cant remember!!

that question was dodgy. how did you work out the price of the pendant (part a)? i had no idea for that part of it.

parko

#### hazza

##### Member
umm

y=b(a^x)

u just had to sub in the values..

#### hazza

##### Member
Originally posted by parko
i think i had something along those lines..........i dunno i didnt write my working in my question booklet, just straight onto the page for that one and now i cant remember!!

that question was dodgy. how did you work out the price of the pendant (part a)? i had no idea for that part of it.

parko

price devide by length

then times that by new length

130/30 = x

#### honky tonk

##### in Miracle World
Originally posted by hazza
130/30 = x
Just to avoid confusion, shouldn't it be 130/30? I thought it varied with the square of 30.

#### parko

##### RN in 2007
ah thankyou guys that makes sense now

parko

#### nikki_ice

##### New Member
umm..u just had to sub in the values

Not that it matters, or that your UAI will automatically be ruined..it is just one question, and you get marks for working out, not especially for getting the right answer...

If you just subbed in the values, then you either get some whacko way out number, or a number that has declined...I think 106 thousand and something sounds alot better after 2 years than so and so to the power of 14...

What is done, is done...this is just a waste of time anyway

#### Gregor Samsa

##### That Guy
Originally posted by honky tonk
Just to avoid confusion, shouldn't it be 130/30? I thought it varied with the square of 30.
I think so. The question specified direct variation to the square of the pendant's length. At first, I mis-read the question and missed that aspect, but fixed it, so the answer was just a matter of figuring out k and then multiplying that by 40 squared.. Hopefully.