z-test or normal distribution
n=20, x̄ =89, s=2.0, 99%
x̄ -z_alpha/2(s/square root of n)< µ< x̄ +z_alpha/2(s/square root of n)
89-(2.575)(2.0/square root of 20)< µ< 89-(2.575)(2.0/square root of 20)
87.848< µ< 90.152
margin of error:
the critical value is 2.575.
the standard deviation is 2.0 (from the question), but as this is a sample, we need the standard error for the mean.
the formula for the se of the mean is standard deviation / √(sample size), so: 2.0/ √(20)=0.447.
me=2.575 * 0.447 = 1.151.
therefore, the margin of error is 1.151 with the confidence interval of 87.848< µ< 90.152.
Please reframe from posting questions that you know the answer to...
The number is 45.
A few ways to do this...but the simplest way I think is to list the two-digit numbers whose tens digit is even and digits add to nine...we have
The only one where the ones digit is one more than the tens digit is 45.
answer by texttutoring(324) About Me (Show Source):
You can put this solution on YOUR website!
Let x= tens digit
Let y = ones digit
Equation 1: x+y = 9
Equation 2: y=x+1
Substitute Equation 2 into Equation 1:
x+ (x+1) = 9
2x + 1 = 9
2x = 8
x = 4
So the tens digit is 4. This means that the ones digit is y =4+1 = 5