Making 2 horizontal buttons fill the screen

Here is the xml

<RelativeLayout xmlns:android="http://ift.tt/nIICcg"
        xmlns:tools="http://ift.tt/LrGmb4"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context="${relativePackage}.${activityClass}" >

    <Button
        android:id="@+id/buttonGnc"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentRight="true"
        android:layout_alignParentTop="true"
        android:text="Güncelle" />

    <ListView
        android:id="@+id/listView1"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:layout_alignParentLeft="true"
        android:layout_below="@+id/Doviz" >

    </ListView>

    **<Button
         android:layout_toLefttOf="@+id/Doviz"
        android:id="@+id/Altin"
        android:layout_width="160dp"
        android:layout_height="wrap_content"
        android:layout_above="@+id/listView1"
        android:layout_alignParentRight="true"
        android:layout_weight="1"
        android:text="Altın" />
    <Button
        android:id="@+id/Doviz"
        android:layout_width="160dp"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_below="@+id/buttonGnc"
        android:layout_weight="1"
        android:text="Döviz" />
</RelativeLayout>**

Ok the buttons whict i want to fill the parent with are Doviz and Altin others are irrelevant.

I tried making width for both of them fill_parent hoping they might get half - half didn't work. I tried giving them width as "0dp" didnt work.

My question is how i can make them(buttons) get the width %50-%50.