Answer:
μd= 1 second
σd= square root (1.25) = √1.25 seconds= 1.1180 seconds
Step-by-step explanation:
Assume that their times are independent. Let DDD be the difference between their times in a random 100-meter dash (D=A-J)(D=A−J)left parenthesis, D, equals, A, minus, J, right parenthesis.
Find the standard deviation of DD
The mean difference is found out by subtracting the individual means.
The mean difference = μd= μA- μJ= 11.5- 10.5= 1 second
The difference standard deviation is given by the square root of sum of the individual variances divided by n. But here n1= n2= 1
σd = sqrt( σ1² / n1 + σ2 ²/ n2 )
First we calculate the variances.
Variance is the square of the standard deviation.
The variance of Andy =σA²= 1²= 1
The variance of Jim =σJ²= (0.5)²= 0.25
The standard deviation difference= σd= √σ²A+ σ²J/1= √1+ 0.25/1= √1.25/1 = √1.25 seconds = 1.1180 seconds
