t-test (independent sample)

An investigation was conducted to find out the effect of water concentration on the amount of oxygen released by hydrilla in a given time. The following data were gathered. 

Table A. Number of oxgen bubbles

Test Tube	Distilled water	Tap water
1	21	19
2	20	18
3	18	17
4	17	19
5	18	20
6	18	20
7	19	20
8	15	21
9	22	29
10	17	21

Here are the steps done to statistically treat the data above:

a. Hypotheses:

Null Hypothesis: X_{distilled water} = X_{tap water}

Alternative: X_{distilled water} ≠ X_{tap water}

b. Significance level: .05

c. Results

Group Statistics

number of oxygen bubbles	type of water	N	Mean	Std. Deviation	Std. Error Mean
	distilled water	10	18.5000	2.06828	.65405
	tap water	10	20.4000	3.27278	1.03494

Independent Samples Test

number of oxygen bubbles	t-test for Equality of Means
	t	df	Sig. (2-tailed)	Mean Difference	Std. Error Difference	95% Confidence Interval of the Difference
	-1.552	18	.138	-1.9000	1.22429	Lower	Upper
						-4.47214	.67214

 The t -vale of -1.552, with degree of freedom of 18 has a significance level of .138, which is greater than the significance level of .05. 

Therefore the null hypothesis is rejected.