SOCR EduMaterials Activities GCLT Applications
Contents
SOCR Educational Materials - Activities - Applications of the General Central Limit Theorem (CLT)
This is a component of the activity is based on the SOCR EduMaterials Activities GeneralCentralLimitTheorem.
Goals
The aims of this activity are to demonstrate several practical applications of the general CLT. There are many practical examples of using CLT to solve real-life problems. Here are some examples which may be solved using the SOCR CLT resources.
The SOCR CLT Experiment
First start by readying carefully the SOCR EduMaterials Activities GeneralCentralLimitTheorem. Then go over each of the CLT applications that are worked out in this activity supplement. You may find it useful going back abd forth between these applications and the formal CLT activity.
Application 1
Suppose a call service center expects to get 20 calls a minute for questions regarding each of 17 different vendors that rely on this call center for handling their calls. What is the probability that in a 1-minute interval they receive less than 300 calls in total?
Let \(X_i\) be the random variable representing the number of calls received about the \(i^{th}\) vendor within a minute, then \(X_i \sim Poisson (20)\), as \(X_i\) is the number of arrivals within a unit interval and the mean arrival count is given to be 20. The distribution of the total number of calls \(T = \sum_{i=1}^{17} \sim Poisson(17 \times 20)\). By CLT, \(T \sim Normal(\mu = 17\times20, \sigma^2 = 17\times20)\), as an approximation of the exact distribution of the total sum. Using the SOCR Distribution applet one can compute exactly the \(P(T<300 | T \sim Poisson(17×20))= 0.014021\). On the other hand side, one may use the CLT to compute a Normal approximation probability of the same event, \(P(T<300 | T \sim Normal(\mu = 17\times20, \sigma^2 = 17\times20)) = 0.014896\). The last quantity is obtained again using the SOCR Distributions applet, without using continuity correction. Using continuity correction the approximation improves, \(P(T<300 | T \sim Normal(\mu = 17\times20, \sigma^2 = 17\times20)) = 0.0140309\). Arguably, the CLT-based calculation is less intense and more appealing to students and trainees, compared to computing the exact probability.
Application 2
It is believed that life-times, in hours, of light-bulbs are Exponentially distributed, say \(Exp({1\over{2,000}})\), mean expected life of 2,000 hours. Recall that the Exponential distribution is called the Mean-Time-To-Failure distribution. You can find more about it from the SOCR Distributions applet. Suppose a University wants to purchase 100 of these light-bulbs and estimate the average life-span of these light bulbs. What is a CLT-based estimate of the probability that the average life-span exceeds 2,200 hrs? Let \(X_i \sim Exp({ 1\over{2,000}})\) and \(\overline{X}= \sum_{i=1}^{100}{X_i}\). Notice that in this case the exact distribution of \(\overline{X}\) is (generally) not Exponential, even though the density may be computed in closed form (Khuong & Kong, 2006). If we use the CLT, however, we can approximate the probability of interest
\(P(\overline{X} > 2,200) \sim P(\overline{X} > 2,200 | \overline{X} \approx N(\mu_{\overline{X}}=2,000, \sigma_{\overline{X}}^2 = {2,000^2 \over 100})),\)
as we know that the mean and the standard deviation of \(X_i\) are \({1\over {\lambda}} =2,000\) and the standard deviation of \(\overline{X}\) is \({1\over {\sqrt{100} \times \lambda}} =200\). Therefore, \(P(\overline{X} >2,200) \approx 0.158655\), using the CLT approximation and the SOCR Distributions calculator, see figure below.
Application 3
Application 4
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