Answer:
The mean depends on the no. of family members but the question hasn't mentioned it. So I have no idea what to do with this.
Answer:

Step-by-step explanation:
Proportion of Heat Loss Between sundown and midnight
Proportion of Heat Loss between midnight and 4 AM 
Proportion of Total Heat Already Lost 
Proportion of Remaining Heat 
Between 4 AM and 5 AM, five-eighths of the remaining heat is lost.
Proportion of Heat Loss between 4 AM and 5 AM= 
Therefore, Proportion of Remaining Heat Left 
We therefore say that:

The number of applicants is 20.
a).The number of ways 20 applicants can be split into two jobs is a question of combination as arrangment is not a necessity in this problem.
b).The number of ways in which 20 applicant can be split into these two jobs categories can be determined as,
Thus, there will be 21 ways in which the jobs can be split into these two categories.
90% of 130 is 117 because 10% is 13 and 13x9 is 117 so that is part a. 130-117 is 13 so that is part b. And part c is correct because 100%-90%=10%. I hope this is helpful.