91Ó°ÊÓ

The gas in bubbles within amber should be a sample of the atmosphere at the time the amber was formed.

Measurements on $9$specimens of amber from the late Cretaceous era ($75to95$ million years ago) give these percents of nitrogen:

$63.465.064.463.354.864.560.849.151.0$

Test for $\mathrm{μ}$:

$\mathrm{μ}$= mean percent of nitrogen in the air during the cretaceous era

Conditions: not a random sample, but representative of air in the cretaceous era independent:$9$samples. $10\%$fall air samples from cretaceous era.

Normal:$n=9<30$

Strong left skew, but no outliers. proceed with caution.

localid="1650695039374" $$\begin{gathered} H_0:\mathrm{μ}=78.1 \\ {H}_a:\mathrm{μ}≠78.1 \\ t=-8.878 \\ p-value=2.05×{10}^{-5} \\ df=8 \end{gathered}$$

We reject$H_0,$because p-value is less than $\mathrm{Î\pm }$. We have sufficient evidence to say the mean percent of nitrogen in the air during the late Cretaceous era was less than $78.1\%.$