stacked_percent_cl.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
  xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:app="http://schemas.android.com/apk/res-auto"
  android:layout_width="match_parent"
  android:layout_height="match_parent">

  <android.support.constraint.Guideline
    android:id="@+id/guideline_50"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:orientation="horizontal"
    app:layout_constraintGuide_percent=".50" />

  <android.support.constraint.Guideline
    android:id="@+id/guideline_80"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:orientation="horizontal"
    app:layout_constraintGuide_percent=".80" />

  <Button
    android:layout_width="0dp"
    android:layout_height="0dp"
    android:text="@string/fifty_percent"

    app:layout_constraintBottom_toTopOf="@id/guideline_50"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="parent" />

  <Button
    android:layout_width="0dp"
    android:layout_height="0dp"
    android:text="@string/thirty_percent"

    app:layout_constraintBottom_toTopOf="@id/guideline_80"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="@id/guideline_50" />

  <Button
    android:layout_width="0dp"
    android:layout_height="0dp"
    android:text="@string/twenty_percent"

    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="parent"
    app:layout_constraintTop_toTopOf="@id/guideline_80" />

</android.support.constraint.ConstraintLayout>