Can't insert correct expression in Average/Mean lesson in Android version

[EskAlam06]

While trying to insert the correct expression in the Average/Mean lesson in Android , it shows error.

Steps-

1. Go to Average/Mean Lesson
2. Try to enter the expression ( see screenshot below)

Expected Behavior- It should work fine and proceed to next question

Actual Behavior- It shows error

Device: Vivo V21 Android Browser: Chrome

Screenshot-