Math Help

Archive for January, 2007

Question: Please help me understand this math(statistics) idea…thanks…?

Hi, in pre-calc, we are learning about statistics. So in our packet, one of the concept is standard value.( the measure of how far away their respective center lie). So in the standard normal distibution chart, 1.3 is appox. 90%. In term of standardized test scores, if i score a percentile of 90%, using that 1.3 standard value- does that mean i am better than 89% of the students who took the test? And there is 20% of people better than me?

But the funny thing is.. my teacher said that i score better than 90% of others….But i find that to be confusing because if i were to score up to the 90%-tile, wouldn’t that mean me proficency is at 90% level and there are 89% ppl and that aren’t in my level??

Please explain this and i am sorry to be confusing…..THANKS!!!!

Answer: too much for 10 points.

asad.

Math Homework Help ( get Math Help Now )

Question: I need a help with a math question. Percent increase?

What is the percent increase from 0 to 1?

Think:

It -IS- possible for something to become 1 from 0.
it -IS- possible to do “the % increase from 50 to 75 is 50%”

So what’s the percent increase from 0 to 1? it’s no infinity. infinity * 0 = 0… or does it?

Thanks in advance =)

Answer: This is one of those questions that teachers dream about not getting. In other words, it’s a great question, but one that is really hard to answer.

Start with your example.

To get the percent increase you do ((75-50)/50)*100. Now look what happens when you try your problem.

((0-1)/0) * 100 =

That’s why we say you cannot divide by zero. You get results that are really strange.

Here’s another example. It is usually shown in a grade 9 or 11 algebra class.

a = b Multiply both sides by a
a*a = b*a Now subtract b*b from both sides
a*a – b*b = b*a – b*b Now factor. You may not have been told how to do this, If not, write me.

(a-b)*(a+b) = b*(a-b) Now divide by the common factor (a-b)
a+b = b Now here’s the kicker. Since a = b you can put in b for the a on the left hand side.

b + b = b. OH OH.
2b = b Now divide by b. No matter what you think the answer on the right is, it’s not 2. In fact you get

2 = 1. Why did that happen? Hint look at the step with a-b divided on both sides.

Zero is the most unruly number in the whole number system. It deserves our utmost respect.

Percentage Increase and Decrease

The mean and variance are some of the most used in math and statistics. Below are some Math Formulas of the mean and variance. 

Estimating the mean – µ

is an unbiased estimator. You can prove this by using:  

If for all n > 1, then the Central Limit Theorem says that: (a Normal distribution). 

Confidence Interval for µ    You can prove this by using:

If the sample is small, to retain 95% CI, you have to widen the interval. To do that, you replace Z _0.025 by t _0.025. Then either: 

and Z 0.025 = 1.96 

OR 

 

If you don’t know for certain, you can use t _0.025 instead of Z to compensate for S.