Help!

Working on a Responsive website using Twitter Bootstrap. The code below works exactly like I want it to in Firefox and Chrome. But the images are not the right size in IE9.

It appears that while in Firefox and Chrome that the image's < width="40%" > specification is displaying the image at 40% of the division's current width (which is the method I want), but that in IE is displaying the image at 40% of the image's original width (which is not what I want).

How do I fix this?

<!-- Horizontal strip of images at the top of the page -->
<div class="container-fluid" style="text-align:center">
<div class="row-fluid">
<div class="span12">
<div class="row-fluid">

<div class="span4">
<img src="picture-one.jpg" width="80%" >
</div>

<div class="span4">
<img src="picture-two.jpg" width="40%" >
<img src="picture-three.jpg" width="40%" >
</div>

<div class="span4">
<img src="picture-four.jpg" width="80%" >
</div>

</div>
</div>
</div>
</div>