(a) A manufacturing engineer is testing a power supply used for machine A. Based on 250 testings, the complete table of observed frequencies are shown in Table Q4. Test the hypothesis whether the output voltage is adequately describes by a normal distribution with mean of 110 V and standard deviation 10 V at a significance level a = 0.05. Table Q4: Observed frequencies for each class interval of power supply. Observed frequencies Class interval X < 90 90 X 100 100 X 110 110 < X < 120 120 < X < 130 X > 130 Total 2 30 85 90 40 3 250 (b) Suppose that when tested on another machine B, the null hypothesis was rejected. List two factors, with explanations, that could lead to the rejection of the null hypothesis.