Question

When I did this problem I got a very small P value and was told it is wrong, I do not know which other test would be appropriate for this question.

Here is a data set containing plant growth measurements of plants grown in solutions of commonly-found chemicals in roadway runoff.

Distilled H2O	Petro	NaCl	MgCl	NaCl + MgCl
19.93	19.85	19.87	19.91	19.73
19.91	20.06	19.88	19.92	19.77
20.08	19.99	20.04	19.84	19.75
19.99	19.88	20.05	19.98	19.93
19.9	19.98	20.06	19.82	19.94
19.98	20.08	19.83	19.92	19.79
19.92	20.1	19.9	20.09	19.84
20.01	19.82	19.83	20.1	19.94
19.96	20.01	19.85	20.04	19.89
20.13	20.1	19.87	20.04	19.72
20.15	19.84	19.85	19.87	19.88
20.04	20.03	19.93	19.89	20
19.98	20.01	19.82	19.77	19.74
20.03	19.96	19.85	19.97	19.95
20.13	19.91	20.06	19.84	19.79
20	20.03	20.04	20.07	19.85
20.07	19.92	20	19.83	19.74
19.98	19.94	19.9	19.9	19.78
20.02	20.01	19.94	19.95	19.88
19.94	19.8	20.05	19.78	19.83

Phragmites australis, a fast-growing non-native grass common to roadsides and disturbed wetlands of Tidewater Virginia, was grown in a greenhouse and watered with either:
    Distilled water (control);
    A weak petroleum solution (representing standard roadway runoff);
    Sodium chloride solution;
    Magnesium chloride solution;
    De-icing brine (50% sodium chloride and 50% magnesium chloride).
Twenty grass preparations were used for each solution, and total growth (in cm) was recorded after watering every other day for 40 days.

-Perform the correct statistical test to determine the p-value.
-Report your answer rounded to four decimal places using scientific notation (ex: 1.2345E-08)
-You should use formulas, functions, and the Data Analysis ToolPak in MS Excel to avoid additive rounding errors. Here are some useful functions:
  =t.test(array1,array2,tails,type)
Produces a p-value for any type of a t-test from a data set
=chidist(x,degrees of freedom)
Produces a p-value from a calculated chi-squared statistic
ANOVA Single Factor from the data analysis tool pack
      Performs a 1-way ANOVA on a data set with only one factor
ANOVA 2-Factor from the data analysis tool pack
         Performs an ANOVA on data with multiple treatments
Regression from the data analysis tool pack
   Performs a linear regression and the corresponding t-test on the slope of the line

___________? (P value)

2) Which of the following is a correct statement of the alternate hypothesis?

Mean growth in the control group is no greater than mean growth in the experimental groups.

Mean growth in the NaCl + MgCl group is less than mean growth in the control group.

Mean growth in the control group is greater than mean growth in the experimental treatments.

Mean growth in one or more of the groups is greater than or less than one of the others.

3) Based on the p-value resulting from your analysis of the Phragmites dataset, which of the following is / are true? (select all that apply)

A post-hoc test is necessary to determine statistically-significant difference(s).

The p-value is greater than ?(0.05).

The p-value is less than ?(0.05).

The calculated F value was less than the critical F value.

The calculated F value was greater than the critical F value.

4) Which is / are (a) proper interpretation(s) of your p-value from your Phragmites data analysis? (select all that apply)

		There is no significant difference in growth between the five groups of Phragmites plants.
		I would fail to reject the null hypothesis.
		I would reject the null hypothesis.
		The control plants' growth rate was greater than the contaminated plants.
		There is a significant difference in growth between the five groups of Phragmites plants.

Answer 1

Seeinf the results of the t tests we conclude

Mean growth in the NaCl + MgCl group is less than mean growth in the control group.

See the left lower part of the second image for the test and upper right part to reject the option a

Mean growth in one or more of the groups is greater than or less than one of the others.

3) Based on the p-value resulting from your analysis of the Phragmites dataset, which of the following is / are true? (select all that apply)

Applied part is The p-value is less than 0.05.

The calculated F value was greater than the critical F value.

4) Which is / are (a) proper interpretation(s) of your p-value from your Phragmites data analysis? (select all that apply)

I would reject the null hypothesis.