Answer
$r\leq lower~critical~value$: null hypothesis is rejected.
There is enough evidence to conclude that the strengths do not fluctuate randomly around the target value of 75 psi.
Work Step by Step
Let's use A if the strength is above 75.
Let's use B if the strength is below 75.
82.0: A
78.3: A
73.5: B
74.4: B
72.6: B
79.8: A
77.0: A
83.4: A
76.2: A
75.2: A
81.5: A
69.8: B
71.3: B
69.4: B
82.1: A
77.6: A
76.9: A
77.1: A
72.7: B
73.6: B
$H_0:~The~sequence~is~random$ versus $H_1:~The~sequence~is~not~random$
$n=20$, $n_A=12$, $n_E=8$ and $r=6$
Small sample case:
$lower~critical~value=6$
$upper~critical~value=16$
(According to table X, for $n_1=12$, $n_2=8$)
Test statistic: $r=6$
Since $r\leq lower~critical~value$, we reject the null hypothesis.
