I want to use the numpad numbers function on my ThinkPad T420 but am unable to activate it.
I have tried to do so by pressing FN+J but this doesn't work.
You can do so by pressing the following key combination:
Fn + NmLk
The NmLk key can be found near the Power On button on your laptop (please refer to the attached picture below.)
When the key combination Fn + NmLk is depressed, an icon will appear on your screen to indicate if the function has been activated.
This means Num Lock is on.
This means Num Lock is off.