4. The strength of beams compared against the moisture content of the beam is indicated in the following table.
| Strength | 21.1 | 22.7 | 23.1 | 21.5 | 22.4 | 22.6 | 21.1 | 21.7 | 21.0 | 21.4 |
| 11.1 | 8.9 | 8.8 | 8.9 | 8.8 | 9.9 | 10.7 | 10.5 | 10.5 | 10.7 |
a. Use your calculator to write down the value of the product moment correlation coefficient for these data.
b. Perform a two-tailed test, at the \(5 \%\) level of significance, to investigate whether there is correlation between strength and moisture content.
c. Use your calculator to write down the equation of the regression line of strength on moisture content.
d. Use the regression line to estimate the strength of a beam that has a moisture content of 9.5.