Aproposed null hypothesis states that there is no difference in the population mean heights of two neighboring districts. the difference of the sample means is 10 cm, and the standard deviation of the difference of sample means is 6 cm. which conclusion can we draw at the 68% confidence level?

a. the population means of the two districts are different.

b. the population means of the two districts are not different.

c. the difference of the sample means of the two districts is 0.

d. the sample means of the two districts are not different.

A. The population means of the two districts are different

State your hypotheses first Null Hypothesis 

Ho: Difference in Population means = 0 

Alternate Hypothesis Ha: Difference in population means is not equal to zero. 

The alternate hypothesis implies we need a two tailed hypothesis test. The empirical rule says that 68% of normally distributed data is within 1 standard deviation of the mean. 

This is also known as the 68-95-99.7 rule. The 68% confidence level gives us the 'fail to reject null hypothesis" region of (-1, 1). But if the test statistic falls outside this interval, we reject the null hypothesis. 

The test statistic z score is z = 10 / ( 6) = 1.67 since your test statistic falls outside the confidence level, we reject the null Hypothesis that there is no difference in the means. So there is evidence to suggest that there is a significant difference in the means.

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answer: decrease

a limiting factor is the one which decrease the abundance, distribution and causes extinction of the population of species in a ecosystem. here, predators including hawks, owls and snakes are the limiting factor for the population of mexican free tailed bat.   although bats are nocturnal animals as they forge for food at night these predators also may remain active during night which can decrease the population of the mexican free-tailed bats. also, these bats eat only one type of insects that are moths. the food can also be a limiting factor as all 400 members are dependent upon same type of food needs that are moths. the decrease in the moth population can cause decrease in population size of the mexican free-tailed bats.

therefore, the scenarios will most likely to decrease the population size of the mexican free-tailed bats.