You want to solve for x so add 18 from both sides of the equal sign. making it 3x=12. then divide both sides by 3 making x=4. x is 4.
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Answer:
Test statistic t=6.505
P-value=0
Step-by-step explanation:
This is a hypothesis test for the population mean.
The claim is that parents tend to underestimate their youngest child's size.
Then, the null and alternative hypothesis are:
The significance level is assumed to be 0.05.
The sample has a size n=39.
The sample mean is M=7.5.
As the standard deviation of the population is not known, we estimate it with the sample standard deviation, that has a value of s=7.2.
The estimated standard error of the mean is computed using the formula:
Then, we can calculate the t-statistic as:
The degrees of freedom for this sample size are:
This test is a right-tailed test, with 38 degrees of freedom and t=6.505, so the P-value for this test is calculated as (using a t-table):
As the P-value (0) is smaller than the significance level (0.05), the effect is significant.
The null hypothesis is rejected.
There is enough evidence to support the claim that parents tend to underestimate their youngest child's size.