We have

of 252 people who have a personalized black disc
Number of people who would have personalized flying disc =

people
Then we work out the number of people who like to play disc golf:

people
So we have 15 people who like to play disc golf and have personalised black disc.

- Error (e) = 50 - 42 = 8 feet
- assumed value (a) = 42 feet

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Answer:
Given:
Sample size, n = 20
Significance level = 5% = 0.05
Mean, u = 8
Here, the sample mean was not given.
Here the null and alternative hypothesis will be:
H0 : u = 8
H1 : u < 8
In this case, since there is no evidence to reject the null hypothesis, H0, at 0.05 level of significance, we can say that the p-value is greater than the level of significance, 0.05.