There are several ways to silence the ringer before answering a call.
Method 1: Press the “Volume Down” or “Volume Up” or “Power” button to mute when an incoming call ring.
Method 2: Go to menu -> “Settings” -> “Sound & vibration”-> activate “Sound off”.
Method 3: Drag the Status Bar down with your finger and then touch the “Media” icon to change to “Vibrate” or “Mute”.
Method 4: Enter “Phone” app and press the menu key in the top right corner of the screen. Then go to “Settings” -> “Sounds and vibration” -> activate “Silent mode”.

Note:

This Q&A question does not apply to the Wi-Fi version of the tablet.

Available settings and menus may vary depending on device model and software version.