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Chapter 7: Q. 1.1 (page 448)

The length of human pregnancies from conception to birth varies according to a distribution that is approximately Normal with mean 266days and standard deviation 16days.

1. Find the probability that a randomly chosen pregnant woman has a pregnancy that lasts for more than 270days. Show your work.

Suppose we choose anSRSof 6 pregnant women. x¯=the mean pregnancy length for the sample.

Short Answer

Expert verified

The probability is 0.4013 .

Step by step solution

01

Given Information

Population mean (μ)=266

Population standard deviation (σ)=16

02

Explanation

The probability that a randomly selected woman has a pregnancy that would be above270days can be calculated as:

localid="1650103880143" P(X>270)=Px-μσ>270-μσ=PZ>270-26616=P(Z>0.25)=0.4013

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Most popular questions from this chapter

According to the U.S. census, the proportion of adults in a certain county who owned their own home was 0.71. An SRS of 100adults in a certain section of the county found that65 owned their home. Which one
of the following represents the approximate probability of obtaining a sample of 100adults in which fewer than 65own their home, assuming that this section of the county has the same overall proportion of adults who own their home as does the entire county?

(a) 10065(0.71)65(0.29)35

(b) 10065(0.29)65(0.71)35
(c) Pz<0.65-0.71(0.71)(0.29)100

(d) Pz<0.65-0.71(0.65)(0.35)100
(e) Pz<0.65-0.71(0.71)(0.29)100

You want to take an SRS 50of the 816students who live in a dormitory on a college campus. You label the students 001to 816in alphabetical order. In the table of random digits, you read the entries

95592 94007 69769 33547 72450 16632 81194 14873

The first three students in your sample have labels

(a) 955,929,400

(b) 400,769,769

(c) 559,294,007

(d) 929,400,769

(e) 400,769,335

identify the population, the parameter, the sample, and the statistic in each setting

Unemployment Each month, the Current Population Survey interviews a random sample of individuals in about 55,000U.S. households. One of their goals is to estimate the national unemployment rate. In December 2009,10.0%of those interviewed were unemployed

Predict the election Just before a presidential election, a national opinion poll increases the size of its weekly random sample from the usual 1500 people to 4000 people.

(a) Does the larger random sample reduce the bias of the poll result? Explain.

(b) Does it reduce the variability of the result? Explain

The Gallup Poll has decided to increase the size of its random sample of voters from about 1500people to about 4000people right before an election. The poll is designed to estimate the proportion of voters who favor a new law banning smoking in public buildings. The effect of this increase is to

(a) reduce the bias of the estimate.

(b) increase the bias of the estimate.

(c) reduce the variability of the estimate.

(d) increase the variability of the estimate.

(e) have no effect since the population size is the same
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