title: layout_weight of LinearLayout for android doesn't work
body: <p>I am new to android and I am working with the linear layout. I want to place an image which takes up 20% of the screen. Here are the codes but this doesn't work.</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:id="@+id/LinearLayout1"
  android:layout_width="fill_parent"
  android:layout_height="fill_parent"
  android:background="@drawable/sky" &gt;
  
  &lt;RelativeLayout
      android:layout_width="fill_parent"
      android:layout_height="fill_parent"
      android:layout_weight="2" &gt;
  
      &lt;ImageView
          android:id="@+id/imageView1"
          android:layout_width="fill_parent"
          android:layout_height="fill_parent"
          android:src="@drawable/schoolroad" /&gt;
  
  &lt;/RelativeLayout&gt;
  
  &lt;RelativeLayout
      android:layout_width="fill_parent"
      android:layout_height="fill_parent"
      android:layout_weight="8" &gt;
  &lt;/RelativeLayout&gt;
  
  &lt;/LinearLayout&gt;
  </code></pre>
  
  <p>The result is that the left layout takes up 80% of the screen.</p>
  
  <p>What's wrong with my codes?</p>