Question: The mean number of students who get first grade in a school of 35 sections is 8 and that of 42 sections of another school is 7. If the variances are 4 and 6, then find out the p-value and verify whether both the means differ at 95% of confidence or not.


A ) 0.0001, the means differ
B ) 0.1922, the means do not differ
C ) 0.0016, the means differ
D ) 0.0488, the means differ

Steps to derive

1 H0: μ1 = μ2 and H1: μ1 ≠ μ2
 [Null and Alternative hypotheses.]

2 X1 = 8, X2 = 7, n1 = 35, n2 = 42, s12 = 4, s22 = 6

3 The z score value is


4 z = 1.972
 [Substitute the values in the z score and simplify.]

5 z = 1.972 occupies an area of 0.4756 under the curve.

6 For 95% confidence level, α = 0.05.

7 P - value = 2(0.5000 - 0.4756) = 0.0488
 [This is a two tailed test.]

8 Since the P value is less that the α value, we reject the null hypothesis.

9 So, there is enough evidence to prove that the mean number of students who got first grade in both the schools differ significantly.



Hence the right answer is Option D

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