Answer: 
Step-by-step explanation:
The confidence interval for population mean is given by :-

Given : Sample size : n= 35 , large sample (n>30)
Mean difference : 
Standard deviation : 
Significance level : 
Critical value : 
Now, the 99.9% confidence interval for the mean difference between the marks scored last week and marks scored this week by all the students will be :-

Hence, the 99.9% confidence interval for the mean difference between the marks scored last week and marks scored this week by all the students = 
9/40 because when you put it in fraction form its 225/1000 then you simplify!
Answer:
55 when y dived and subtracting
Step-by-step explanation:
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x=2y is linear and can also be writtend as y=x/2
Answer:
A
Step-by-step explanation:
I am not sure though. Sorry if it is wrong :(