<p>Let’s say you are managing products for an eCommerce store. You think products from <em>category 9</em> have a lower average price than those in all other categories.</p>

<p>Calculate the t-value and degrees of freedom for such a test. You do not need to calculate the p-value of the test.</p>

<p><strong>Example:</strong></p>

<p><strong>Input:</strong></p>

<p><code>products</code> table</p>

<table>
<thead>
<tr>
<th>Column</th>
<th>Type</th>
</tr>
</thead>

<tbody>
<tr>
<td><code>id</code></td>
<td>INTEGER</td>
</tr>

<tr>
<td><code>name</code></td>
<td>VARCHAR</td>
</tr>

<tr>
<td><code>price</code></td>
<td>DOUBLE</td>
</tr>

<tr>
<td><code>category_id</code></td>
<td>INTEGER</td>
</tr>
</tbody>
</table>
<p><strong>Output</strong></p>

<table>
<thead>
<tr>
<th>Column</th>
<th>Type</th>
</tr>
</thead>

<tbody>
<tr>
<td><code>t_value</code></td>
<td>DOUBLE</td>
</tr>

<tr>
<td><code>d_o_f</code></td>
<td>INTEGER</td>
</tr>
</tbody>
</table>


t Value via SQL

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