# What is the value of the estimate of the common variance?

**Question description**

A lab scientist is interested in whether lab rats that grow up alone grow as large as lab rats that grow up with other rats around them to play with. He randomly selects 10 young rats with approximately the same age and size. Five of these will spend the next four monthsalone and the other five rats will each have three other rats to play with during the same time. After four months, the scientist measures the abdomen circumference of all the rats (in mm). The results are shown below:

Alone group (#1) |
110 |
123 |
113 |
103 |
120 |

Play group (#2) |
119 |
125 |
131 |
128 |
136 |

The sample means and sample standard deviations are

= 113.8 and *s*_{1} =
7.98, = 127.8 and *s*_{2} =
6.38

What is the value of the estimate of the common variance?

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