Answer:
<em> The calculated value Z = 1.8823 <1.96 at 0.05 level of significance</em>
<em> The average amount of energy used in his factory per day has changed since last year. </em>
Step-by-step explanation:
<u><em>Step(i):-</em></u>
Given that mean of the Population = 2000 (MWH)
Given that size of the sample 'n' = 400
Given that mean of sample x⁻ = 2040 MWH
Given that the standard deviation = 425 MWH per day
<u><em>Step(ii):-</em></u>
<u><em>Null hypothesis:H₀: μ = 2000 (MWH)</em></u>
<u><em>Alternative Hypothesis:H₁: μ≠ 2000( MWH)</em></u>
<em>Test statistic</em>
<em> </em><em></em>
<em> </em><em></em>
<em> Z = 1.8823</em>
<em>The calculated value Z = 1.8823 <1.96 at 0.05 level of significance</em>
<u><em>Final answer:</em></u><em>-</em>
<em> The calculated value Z = 1.8823 <1.96 at 0.05 level of significance</em>
<em> The average amount of energy used in his factory per day has changed since last year. </em>