XML Linear Vahy Android

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
    <Button
        android:text="50%"
        android:layout_width="fill_parent"
        android:layout_height="0dip"
        android:layout_weight="50"
    />
    <Button
        android:text="30%"
        android:layout_width="fill_parent"
        android:layout_height="0dip"
        android:layout_weight="30"
    />
    <Button
        android:text="20%"
        android:layout_width="fill_parent"
        android:layout_height="0dip"
        android:layout_weight="20"
    />
</LinearLayout>