If you want to limit the user into choosing a numerical value from a specific range, you can simply do it by setting the MinValue and MaxValue
properties. Here is an example.
CopyXAML
<telerikInput:RadNumericUpDown x:Name="radNumericUpDown" VerticalAlignment="Center" MinValue="10" MaxValue="20" Value="10" />
This will prevent the user from selecting a value of this range.