Help Me!!!

Test Preparation SAT Preparation
1

<p>I don't understand how to this stupid question and it is getting on me nerves. I hate this test. STupid SATS. OK here goes</p>

<p>If a population that is initially 100 triples every year, which of the following is an expression for the size of the population after t months?
a. 100<em>3^t
b. 100</em>12^3t
c. 100<em>3^(t/12)
d. 100</em>3^(12/t)
e. 100*3^12t</p>

<p>When i did this problem I got an answer of (100)*(3)^((t/12)-1)
I used the geometric sequence formula ar^(n-1)</p>

<p>Did I do anything wrong? If i did, how do i get the right answer?</p>

2

<p>Thanks everyone for your help when you get around to reading this. Woot this is my second post. I am getting somewhere. LOL</p>

3

<p>The answer is C.</p>

<p>After 12 months, population goes from 100->300</p>

<p>100*3^(12/12) = 300</p>

<p>After 24 months, population goes from 300 -> 900</p>

<p>100*3^(24/12) = 900</p>

<p>and for good luck</p>

<p>36 months has to go from 900->2700</p>

<p>100*3^(36/12) = 2700</p>

4

<p>Thanks for the help. But does anyone know how to recieve this solution algebriacallu, not by guessing?</p>

5

<p>can anyone answer my question?</p>

6

<p>It's not really much algebra, you just have to have a basic understanding of exponential functions. The basic form is</p>

<p>Pr^x
P is what you start with, in this case 100
r is what the number is multiplied by, in this case 3 (since it triples).
x is the amount of time the population is growing for. And since it's multiplied by 3 every YEAR, x must be in YEARS. But this problem wants it in months. And one month = 1/12 of a year. So if you want to talk about "t months" (which the problem asks for), you instead must say "t/12", because you're converting months into years.</p>

<p>So you plug that in, and get 100*3^(t/12).</p>

7

<p>on the SAT I you never need formulas such as ar^(n-1). chances are, if you are using these formulas, you are overcomplicating the problem.</p>

<p>thecomisar had the most methodical answer, but alvy had a good approach if you didn't see the method right away: substitution! it works wonders on so many SAT I problems.</p>

<p>now the SAT II, there your formula will be useful.</p>

8

<p>Yeah, I would definitely do what alvy did (plug in numbers) to check the problem.</p>

9

<p>thank you all for the help and the answer is C, just like everyone said. Thanks for the explanations.</p>

10

<p>re: OP - it's not guessing it's just approaching the problem in the quickest way possible.</p>