I added a linearlayout for imageview and progress bar and gave it 0dp height and 70 weight.
Also notice that parent linearlayout has a weightsum set to 100.
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@android:color/black">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" android:weightSum="100">
<LinearLayout
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="70"
android:orientation="vertical">
<ImageView
android:id="@+id/appLogo"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:src="@drawable/logo"/>
<ProgressBar
android:id="@+id/progressbar"
android:indeterminate="true"
android:layout_width="50dp"
android:layout_height="50dp"
style="?android:attr/progressBarStyle"
android:indeterminateBehavior="cycle"
android:layout_centerHorizontal="true"
android:layout_gravity="center_vertical|center_horizontal"/>
</LinearLayout>
<ScrollView
android:layout_width="fill_parent"
android:layout_height="0dp"
android:layout_weight="30">
<LinearLayout
android:id="@+id/startLayout"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:gravity="center"
android:orientation="vertical"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin">
</LinearLayout>
</ScrollView>
</LinearLayout>
</RelativeLayout>