teekayy wrote:Students are taking their test, and those who score in the bottom 16 percent will have to retest. If the scores are normally distributed and the mean is 72, what is the score at or below which the students have to retest?
(1) there are 500 students in the class
(2) 10 students scored 82 or higher
answer: C
The normal distribution, also called the Gaussian distribution, is an important family of continuous probability distributions, applicable in many fields. Each member of the family may be defined by two parameters, location and scale: the mean ("average", μ) and variance (standard deviation squared, σ2) respectively. The standard normal distribution is the normal distribution with a mean of zero and a variance of one (the red curves in the plots to the right). Carl Friedrich Gauss became associated with this set of distributions when he analyzed astronomical data using them,[1] and defined the equation of its probability density function. It is often called the bell curve because the graph of its probability density resembles a bell.
This question needs some background information. Whenever you see 16%, you always remember Gaussian
Statement 1) Just gives us the sample size - Insuf
Statement 2) 10 students scored 82 or higher - Insuf - We need to know how many more students we have
1&2
Min - 10 Students - 62 - 240 students MEAN (72) - 240 students - 82 -1o students - Max
You can find the bottom 16 %, but again this is a MATH question, not a GMAT question.
If anybody knows a GMAT solution, I really want to learn otherwise, I can bore you with calculations:
Please refer to:
https://en.wikipedia.org/wiki/Normal_distribution
