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<title>Using Rational Numbers</title>
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<h1 class="center">Using Rational Numbers</h1>
<p class="center">How to add, subtract, multiply and divide rational numbers</p>
<p>A <a href="../rational-numbers.html">rational number</a> is a number that can be written as a simple fraction (i.e. as a <b>ratio</b>).</p>
<h3>Examples:</h3>
<div class="simple">
<table width="400" border="0" align="center">
<tr align="center">
<th>Number</th>
<th>As a Fraction</th>
</tr>
<tr align="center">
<td height="9">5</td>
<td height="9">5/1</td>
</tr>
<tr align="center">
<td height="9">1.75</td>
<td height="9">7/4</td>
</tr>
<tr align="center">
<td>.001</td>
<td>1/1000</td>
</tr>
<tr align="center">
<td>0.111...</td>
<td>1/9</td>
</tr>
</table>
<h2>In general ...</h2> </div>
<p>So a rational number looks like this:</p>
<p class="center large"><span class="intbl"><em>p</em><strong>q</strong></span></p>
<p>But q cannot be zero, as that is <a href="../numbers/dividing-by-zero.html">dividing by zero</a>.</p>
<h2>How to Add, Subtract, Multiply and Divide</h2>
<p>When the rational number is something simple like <b>3</b>, or <b>0.001</b>, then just use mental arithmetic, or a calculator!</p>
<p><b>But what about when it is in <span class="center large"><span class="intbl"><em>p</em><strong>q</strong></span></span> form? </b></p>
<div class="beach">
<table style="border: 0; margin:auto;">
<tr>
<td align="center" valign="top"><span class="huge"><br>
&frac12;</span></td>
<td>&nbsp;</td>
<td>
<p>Well, a rational number is a <a href="../fractions-menu.html">fraction</a>, so we can use:</p>
<ul>
<li><a href="../fractions_addition.html">Adding Fractions</a>,</li>
<li><a href="../fractions_subtraction.html">Subtracting Fractions</a>,</li>
<li><a href="../fractions_multiplication.html">Multiplying Fractions</a> and</li>
<li><a href="../fractions_division.html">Dividing Fractions</a>&nbsp;</li>
</ul>
</td>
</tr>
</table>
</div>
<p><b>Here we will see those operations in a more general <a href="index.html">Algebra</a> style.</b></p>
<p>You might also like to read <a href="fractions-algebra.html">Fractions in Algebra</a>.</p>
<p>Let us start with multiplication, as that is the easiest.</p>
<h2>Multiplication</h2>
<p>To multiply two rational numbers <b>multiply the tops and bottoms separately</b>, like this:</p>
<script>
playerMain("images/rational-mult-a.txt", 600, 140);
</script>
<p>Here is an example:</p>
<script>
playerMain("../numbers/images/fractions-mult-a.txt", 600, 160);
</script>
<h2>Division</h2>
<p>To divide two rational numbers, first flip the second number over (make it a reciprocal) and then do a multiply like above:</p>
<script>
playerMain("images/rational-div-a.txt", 600, 200);
</script>
<p>Here is an example:</p>
<script>
playerMain("../numbers/images/fractions-div-a.txt", 630, 140);
</script>
<h2>Addition and Subtraction</h2>
<p>We will cover Addition and Subtraction in one go, as they are the same method.</p>
<p>Before we add or subtract, the rational numbers should have the <b>same bottom number</b> (called a <a href="../numbers/common-denominator.html">Common Denominator</a>).</p>
<p>The easiest way to do this is to</p>
<p class="center"><span class="large">Multiply both parts of each number by the bottom part of the other</span></p>
<p>Like this (note that the dot <span class="large"> &middot; </span> means multiply):</p>
<script>
playerMain("images/rational-add-a.txt", 620, 220);
</script>
<p>Here is an example of addition:</p>
<script>
playerMain("images/rational-add-b.txt", 600, 200);
</script>
<p>And an example of subtraction (the middle step is skipped to make it quicker):</p>
<script>
playerMain("images/rational-add-c.txt", 620, 140);
</script>
<h2>Simplest Form</h2>
<p>Sometimes we have a rational number like this:</p>
<p class="center large"><span class="intbl"><em>10</em><strong>15</strong></span></p>
<p>But that is not as simple as it can be!</p>
<p>We can divide both top and bottom by 5 to get:</p>
<table style="border: 0; margin:auto;">
<tr>
<td align="center" class="large">&divide; 5</td>
</tr>
<tr>
<td align="center"><img src="../images/style/right-over-arrow.gif" width="75" height="25" alt="right over arrow" /></td>
</tr>
<tr>
<td align="center"><span class="large"><span class="intbl"><em>10</em><strong>15</strong></span> &nbsp; = &nbsp; <span class="intbl"><em>2</em><strong>3</strong></span></span>
</td>
</tr>
<tr>
<td align="center"><img src="../images/style/right-under-arrow.gif" width="75" height="25" alt="right under arrow" /></td>
</tr>
<tr>
<td align="center" class="large">&divide; 5</td>
</tr>
</table>
<p>Now it is in &quot;simplest form&quot;, which is how most people want it!</p>
<h2>Be Careful With &quot;Mixed Fractions&quot;</h2>
<p>We may be tempted to write an <a href="../improper-fractions.html">Improper Fraction</a> (a fraction that is &quot;top-heavy&quot;, i.e. where the top number is bigger then the bottom number) as a <a href="../mixed-fractions.html">Mixed Fraction</a>:</p>
<p>For example <span class="frac"><sup>7</sup>/<sub>4</sub></span> = 1 <span class="frac"><sup>3</sup>/<sub>4</sub></span>, shown here:<br></p>
<table style="border: 0; margin:auto;">
<tr align="center">
<td><span class="large"><img src="../images/style/yes.svg" alt="yes" width="48" /><br>
Improper Fraction</span></td>
<td>&nbsp;</td>
<td><span class="large"><img src="../images/style/no.svg" alt="not" width="48" /><br>
Mixed Fraction</span></td>
</tr>
<tr align="center">
<td><span class="frac-large"><sup>7</sup>/<sub>4</sub></span> </td>
<td width="40">&nbsp;</td>
<td><span class="large">1</span> <span class="frac-large"><sup>3</sup>/<sub>4</sub></span> </td>
</tr>
<tr align="center">
<td><img src="../images/fractions/pie-4-4.jpg" alt="4/4" width="120" height="120" /><img src="../images/fractions/pie-3-4.jpg" alt="3/4" width="120" height="120" /></td>
<td width="40" class="large">=</td>
<td><img src="../images/fractions/pie-1-1.jpg" width="120" height="120" alt="pie full" /><img src="../images/fractions/pie-3-4.jpg" alt="3/4" width="120" height="120" /></td>
</tr>
</table>
<p>But for mathematics the &quot;Improper&quot; form (such as <span class="frac"><sup>7</sup>/<sub>4</sub></span>) is actually <b>better</b>.</p>
<p>Because Mixed fractions (such as 1 <span class="frac"><sup>3</sup>/<sub>4</sub></span>) can be confusing when we write them down in a formula, as it can look like a <b>multiplication</b>:</p>
<table style="border: 0; margin:auto;">
<tr>
<th align="right">Mixed Fraction: </th>
<th>&nbsp;</th>
<td align="right">What is:&nbsp;</td>
<td>1 + 2<span class="intbl"><em>1</em><strong>4</strong></span> ?</td>
</tr>
<tr>
<td align="right">&nbsp;</td>
<td>&nbsp;</td>
<td align="right">Is it:&nbsp;</td>
<td>1 + 2<span class="hilite"> + </span> <span class="intbl"><em>1</em><strong>4</strong></span> = 3<span class="intbl"><em>1</em><strong>4</strong></span> <b class="large">?</b></td>
</tr>
<tr>
<td align="right">&nbsp;</td>
<td>&nbsp;</td>
<td align="right"><i>Or</i> is it:&nbsp;</td>
<td>1 + 2<span class="hilite"> &times; </span> <span class="intbl"><em>1</em><strong>4</strong>
</span> = 1<span class="intbl"><em>1</em><strong>2</strong></span> <b class="large">?</b></td>
</tr>
<tr>
<td align="right">&nbsp;</td>
<td>&nbsp;</td>
<td align="right">&nbsp;</td>
<td>&nbsp;</td>
</tr>
<tr>
<th align="right">Improper Fraction: </th>
<th>&nbsp;</th>
<td align="right">What is:&nbsp;</td>
<td>1 + <span class="intbl"><em>9</em><strong>4</strong></span> ?</td>
</tr>
<tr>
<td align="right">&nbsp;</td>
<td>&nbsp;</td>
<td align="right">It is:&nbsp; </td>
<td><span class="intbl"><em>4</em><strong>4</strong></span> + <span class="intbl"><em>9</em><strong>4</strong></span> = <span class="intbl"><em>13</em><strong>4</strong></span> &nbsp;<img src="../images/style/yes.svg" alt="yes" /></td>
</tr>
</table>
<p>So try to use the <b>Improper Fraction</b> when doing mathematics.</p>
<p>&nbsp;</p>
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