Answer: 5.37
Step-by-step explanation:
Let x = ACT scores.
Given: ACT scores have a mean of 20.8 and 9 percent of the scores are above 28. The scores have a distribution that is approximately normal.
i.e. P(X>28)=0.09 (i)
Now,
(ii)
One -tailed z value for p-value of 0.09 =1.3408 [By z-table]
From (i) and (ii)

Hence, the standard deviation = 5.37
Answer:
78.40
Step-by-step explanation:
Take 9.80 and times it by 8 to get 78.40
Let James be x years old
Joe = 10 + x
After 8 years
18 + x = 3(x)
18 + x = 3x
18 = 2x
x = 9
Joe is 19
James is 9