title: Layout issue on multiple devices
body: <p>As we know we can create a single layout for all type of devices by using size in dp.  i have created a xml with dp but it is displaying different on every other device like 7' , 10' tab, 5.4, 5.1 3.7 etc.</p>
  
  <p>i have placed file in "layout"  folder and now to support all these device i have to create different layout folder for all devices and it is tough to maintain, even i have created a hdpi,xhdpi etc as well but still lots of layout is need to create. please find below xml:</p>
  
  <pre><code>&lt;RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:ads="http://schemas.android.com/apk/lib/com.google.ads"
    android:id="@+id/ans4"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:background="@drawable/bg_orange"
  tools:context="com.kids.kidsmath.MainActivity"
  tools:ignore="MergeRootFrame" &gt;
  
  &lt;Button
      android:id="@+id/mathCalculation"
      android:layout_width="250dp"
      android:layout_height="40dp"
      android:layout_alignParentTop="true"
      android:layout_centerHorizontal="true"
      android:layout_marginTop="104dp"
      android:background="@drawable/curve_shape"
      android:onClick="openMa"
      android:text="Play "
      android:textColor="#000000"
      android:textSize="20sp"
      android:textStyle="bold"
      android:typeface="sans" /&gt;
  
  &lt;Button
      android:id="@+id/learnCounting"
      android:layout_width="250dp"
      android:layout_height="40dp"
      android:layout_alignLeft="@+id/mathCalculation"
      android:layout_alignRight="@+id/mathCalculation"
      android:layout_below="@+id/mathCalculation"
      android:layout_marginTop="46dp"
      android:background="@drawable/curve_shape"
      android:onClick="openL"
      android:text="Lg"
      android:textColor="#000000"
      android:textSize="20sp"
      android:textStyle="bold"
      android:typeface="sans" /&gt;
  
  &lt;Button
      android:id="@+id/greatersmaller"
      android:layout_width="250dp"
      android:layout_height="40dp"
      android:layout_alignLeft="@+id/learnCounting"
      android:layout_alignRight="@+id/learnCounting"
      android:layout_below="@+id/learnCounting"
      android:layout_marginTop="40dp"
      android:background="@drawable/curve_shape"
      android:onClick="openS"
      android:text="Gr"
      android:textColor="#000000"
      android:textSize="20sp"
      android:textStyle="bold"
      android:typeface="sans" /&gt;
  
  
  &lt;/RelativeLayout&gt;
  </code></pre>
  
  <p>please help me if i m doing wrong in this xml. also do we need to define different xml for all?</p>