Final answer:
To find the t-test statistic, subtract the population mean from the sample mean and divide by the standard error. With a sample mean of 40.1, a population mean of 42, and a standard error of 2.5, the t-test statistic is -0.76.
Step-by-step explanation:
To calculate the t-test statistic for this scenario where the sample average is 40.1 and the null hypothesis population mean is 42, with a standard error of 2.5, we use the formula for the t-statistic:
t =

Where:
is the sample mean,
is the population mean under the null hypothesis, and- SE is the standard error.
Plugging in our values:
t = (40.1 - 42) / 2.5
t = -1.9 / 2.5
t = -0.76
Therefore, the t-test statistic is -0.76 (rounded to four decimal places).