I can't understand whats causing this, although math has never been my specialty so any help is appreciated. My simple equation is in two parts:

Answer 1) 226 - [value] multiplied by .9

Answer 2) 226 - [value] multiplied by .55

If you use 40 as the input value, my calculator says:

Answer 1) 226 - 40 = 186 * .9 = 167.4

Answer 2) 226 - 40 = 186 * .55 = 102.3

But my code says:

Answer 1) 190

Answer 2) 204

My Code:

HTML:
<input id="HR"size="4" value="" /><span id="number"></span>
 Answer 1 <strong><span id="answer1"></span></strong><br>
 Answer 2 <strong><span id="answer2"></span></strong>
</p>

<a href="#" class='THR'>click to calculate</a>

Script:
 <script type="text/javascript">
     $('a.THR').click(function() {
     var value = parseInt( $( "#HR" ).val() );
     $( "#answer1" ).html( 226 - value * 0.9 );
     $( "#answer2" ).html( 226 - value * 0.55 );
     return false;
   });
 </script>

I can't understand whats causing this, although math has never been my specialty so any help is appreciated. My simple equation is in two parts:

Answer 1) 226 - [value] multiplied by .9

Answer 2) 226 - [value] multiplied by .55

If you use 40 as the input value, my calculator says:

Answer 1) 226 - 40 = 186 * .9 = 167.4

Answer 2) 226 - 40 = 186 * .55 = 102.3

But my code says:

Answer 1) 190

Answer 2) 204

My Code:

HTML:
<input id="HR"size="4" value="" /><span id="number"></span>
 Answer 1 <strong><span id="answer1"></span></strong><br>
 Answer 2 <strong><span id="answer2"></span></strong>
</p>

<a href="#" class='THR'>click to calculate</a>

Script:
 <script type="text/javascript">
     $('a.THR').click(function() {
     var value = parseInt( $( "#HR" ).val() );
     $( "#answer1" ).html( 226 - value * 0.9 );
     $( "#answer2" ).html( 226 - value * 0.55 );
     return false;
   });
 </script>

• javascript
• math

• Note that the statement 226 - 40 = 186 * .9 is also simply incorrect. – pimvdb Commented Sep 1, 2011 at 20:26

6 Answers 6

You are forgetting order of operations. Multiplication has higher precedence than addition/subtraction. Put parenthesis around your 226-value

 $( "#answer1" ).html( (226 - value) * 0.9 );
 $( "#answer2" ).html( (226 - value) * 0.55 );

Rereading your question, I'm not sure what exactly your desired result is. If you want to do the multiplication first and then the subtraction, you don't need the parenthesis, though it may be helpful to write 226 - (value * 0.9) to make it clear. What is happening on your calculator though is that you are typing 226 - value and then multiplying that result by your decimal number. So the above code, (226 - value) * 0.9, represents your typing. It may help to describe what you are trying to do from the end user's perspective to decide where your parentheses go.

Parentheses: you need them.

 $( "#answer1" ).html( (226 - value) * 0.9 );
 $( "#answer2" ).html( (226 - value) * 0.55 );

Multiplication takes precedence over substraction.
Hence the expressions will be interpreted as:

Answer 1) 226 - ([value] multiplied by .9 )
e.g:

226 - (40 *0.9) = 226 - 36 = 190

Answer 2) 226 - ([value] multiplied by .55)
e.g:

226 - (40 * .55) = 226 - 22 = 204

You're code is honoring the standard order of operations:

• Parentheses,
• Exponeniation,
• Multiplcation/Division
• Addition/Subtraction

...but you are not. Parenthesize your equation to change the order to what you want.

This is just an order-of-operations issue (nothing to do with jquery). Multiplication/division is performed before addition/subtraction. So:

226 - 40*.9 = 226 - 36 = 190

In math, multiplication takes precedence over addition and subtraction. Use parentheses to clarify:

$( "#answer1" ).html( (226 - value) * 0.9 );
$( "#answer2" ).html( (226 - value) * 0.55 );