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The total brain volume (in ${\text{cm}}^3$) of 20 twins is proved in the dataset.

The mean volume is equal to 1126.0 ${\text{cm}}^3$.

The standard deviation is equal to 124.9 ${\text{cm}}^3$.

The significant values of mathematical data can be identified using the range rule of thumb, which states that values

• equal to or less than$渭-蟽$ are considered to be significantly low values.
• equal to or greater than$渭+蟽$ are considered to be significantly high values.
• between $渭-蟽$and $渭+蟽$ are not considered to be significant values.

Here, $渭$stands for the mean of the data, and $蟽$stands for the standard deviation of the data.

So, the limits become as shown below:

Lower limit:

$$\begin{gathered} 渭-2蟽=1126.0-2脳124.9 \\ =1126.0-249.8 \\ =876.2 \end{gathered}$$.

Upper limit:

.$$\begin{gathered} 渭+2蟽=1126+2脳124.9 \\ =1126+249.8 \\ =1375.8 \end{gathered}$$

For the given brain volumes, the limit-separating values are , which implies that the values below 876.2 ${\text{cm}}^3$are significantly low, and those above 1375.8 ${\text{cm}}^3$are significantly high.

If the value lies between the limits, it is not significant, and if it lies beyond the limits, it is significant.

The total brain volume equal to 1440${\text{cm}}^3$ lies beyond the upper limit of 1375.8${\text{cm}}^3$ . Therefore, it is significantly high.