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http://www.mathsisfun.com/operation-order-pemdas.html
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Order of Operations
Do things in Parentheses First. Example:
<table align="center" border="0" cellpadding="3" width="370"><tbody><tr><td class="Larger">
</td><td class="Larger">
</td><td class="Larger">6 × (5 + 3)</td><td class="Larger">=</td><td class="Larger">6 × 8</td><td class="Larger">=</td><td class="Larger">
48
</td><td class="Larger">
</td></tr><tr><td class="Larger">
</td><td class="Larger">
</td><td class="Larger">6 × (5 + 3) </td><td class="Larger">=</td><td class="Larger">
30 + 3</td><td class="Larger">=</td><td class="Larger">
33
</td><td class="Larger">(wrong)</td></tr></tbody></table>
Exponents (Powers, Roots) before Multiply, Divide, Add or Subtract. Example:
<table align="center" border="0" cellpadding="3" width="370"><tbody><tr><td class="Larger">
</td><td class="Larger">
</td><td class="Larger">5 × 2<sup>2</sup></td><td class="Larger">=</td><td class="Larger">5 × 4</td><td class="Larger">=</td><td class="Larger">
20
</td><td class="Larger">
</td></tr><tr><td class="Larger">
</td><td class="Larger">
</td><td class="Larger">5 × 2<sup>2</sup></td><td class="Larger">=</td><td class="Larger">
10<sup>2</sup></td><td class="Larger">=</td><td class="Larger">
100
</td><td class="Larger">(wrong)</td></tr></tbody></table>
Multiply or Divide before you Add or Subtract. Example:
<table align="center" border="0" cellpadding="3" width="370"><tbody><tr><td class="Larger">
</td><td class="Larger">
</td><td class="Larger">2 + 5 × 3</td><td class="Larger">=</td><td class="Larger">2 + 15</td><td class="Larger">=</td><td class="Larger">
17
</td><td class="Larger">
</td></tr><tr><td class="Larger">
</td><td class="Larger">
</td><td class="Larger">2 + 5 × 3 </td><td class="Larger">=</td><td class="Larger">
7 × 3</td><td class="Larger">=</td><td class="Larger">
21
</td><td class="Larger">(wrong)</td></tr></tbody></table>
Otherwise just go left to right. Example:
<table align="center" border="0" cellpadding="3" height="72" width="370"><tbody><tr><td class="Larger">
</td><td class="Larger">
</td><td class="Larger">30 ÷ 5 × 3 </td><td class="Larger">=</td><td class="Larger">6 × 3</td><td class="Larger">=</td><td class="Larger">
18
</td><td class="Larger">
</td></tr><tr><td class="Larger">
</td><td class="Larger">
</td><td class="Larger">30 ÷ 5 × 3 </td><td class="Larger">=</td><td class="Larger">30 ÷
15</td><td class="Larger">=</td><td class="Larger">
2
</td><td class="Larger">(wrong)</td></tr></tbody></table>