A researcher is interested in estimating the mean weight of a semi tracker tractor truck to determine the potential load capacity. She takes a random sample of 17 trucks and computes a sample mean of 20,000 pounds with sample standard deviation of 1,500. The 95% confidence interval for the population mean weight of a semi tracker tractor truck is .

(19228.737 ; 20771.263)

Step-by-step explanation:

Given that:

Sample size, n = 17

Sample mean, m = 20,000

Sample standard deviation, s = 1500

α = 95%

The confidence interval,

Mean ± margin of error

Margin of Error : Tcritical * s/sqrt(n)

Tcritical at α = 0.05 ; df = n-1 = 17 - 1 = 16 ; 2 - tailed test = 2.120

Margin of Error = 2.120 * 1500/sqrt(17) = 771.263

Lower boundary :

20,000 - 771.263 = 19228.737

Upper boundary :

20,000 + 771.263 = 20771.263

Confidence interval :

(19228.737 ; 20771.263)

x = -3

y = -18

step-by-step explanation:

to solve by substitution, substitute one variable and solve for the other. then substitute again to find the remaining variable.

x-1/3(3x-9) = -3 since y=3x-9 substittute y.

x-1/3(3x-9)=-3

x + x +3 = -3

2x+3=-3

2x+3-3= -3-3

2x=-6

x=-3

substitute again into y=3x-9

y=3(-3)-9

y=-9-9

y=-18