Which of the following Read-only service-defined variables would you use in the AutoScale formula when you want scaling depending upon the number of tasks that are running at a specific point in time?

Answer options:

A.$ActiveTasks
B.$RunningTasks
C.$SucceededTasks
D.$PendingTasks

Correct Answer: B 
$RunningTasks variable should be used while scaling depending upon the number of tasks running at a point in time.
Option A is incorrect. $ActiveTasks variable is used when scaling depending upon the number of tasks that are queued up to run.
Option B is correct. $RunningTasks variable should be used when scaling depending upon the number of tasks running at a point in time.
Option C is incorrect. $SucceededTasks is used for the number of tasks completed successfully.
Option D is incorrect. $PendingTasks is used for the number of tasks that are queued or running.
Reference: 
To know more about creating automatic formulas, please visit the following link: 

https://docs.microsoft.com/en-us/azure/batch/batch-automatic-scaling