The accompanying table gives summary data on cube compressive strength (N/mm2) for concrete specimens made with a pulverized fuel-ash mix. Age (days)     Sample     Size     Sample     Mean     Sample     SD 7     69 26.94 4.84 28     71 35.77 6.46 Calculate a 99% CI for the difference between true average 7-day strength and true average 28-day strength. (Use H0: ?7 − ?28 = 0. Round your answers to two decimal places.)     ,       N/mm2   Determine the number of degrees of freedom for the two-sample t test or CI in each of the following situations. (Round your answers down to the nearest whole number.) (a)    m = 12, n = 10, s1 = 5.0, s2 = 6.0   (b)    m = 12, n = 15, s1 = 5.0, s2 = 6.0   (c)    m = 12, n = 15, s1 = 4.0, s2 = 6.0   (d)    m = 10, n = 24, s1 = 5.0, s2 = 6.0

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The accompanying table gives summary data on cube compressive strength (N/mm2) for concrete specimens made with a pulverized fuel-ash mix.

Age
(days)
    Sample    
Size
    Sample    
Mean
    Sample    
SD
7     69 26.94 4.84
28     71 35.77 6.46

Calculate a 99% CI for the difference between true average 7-day strength and true average 28-day strength. (Use H0: ?7 − ?28 = 0. Round your answers to two decimal places.)

 
   ,   
 

 N/mm2

 

Determine the number of degrees of freedom for the two-sample t test or CI in each of the following situations. (Round your answers down to the nearest whole number.)

(a)    m = 12, n = 10, s1 = 5.0, s2 = 6.0
 

(b)    m = 12, n = 15, s1 = 5.0, s2 = 6.0
 

(c)    m = 12, n = 15, s1 = 4.0, s2 = 6.0
 

(d)    m = 10, n = 24, s1 = 5.0, s2 = 6.0
Expert Solution
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Hi! Thank you for the question. As per the honor code, we are allowed to answer 1 question at a time, so we are answering the first question as you have not mentioned which of these you are looking for. Please re-submit the question separately for the remaining questions.

Let μ7 and σ7 denote respective the population mean and standard deviation for 7-day strength.

Let μ28 and σ28 denote respective the population mean and standard deviation for 28-day strength.

Given that n7=69, x¯7=26.94, s7=4.84, n28=71, x¯28=35.77, s28=6.46, confidence level=0.99.



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