What is the correct form and what is the exact name of this phenomenon. I tried looking it up myself but I could only find a German explanation that might also explain the English problem.
An example could be:
Please read page 1 and 2
vs
Please read pages 1 and 2
or
I like number 2 and 3
vs
I like numbers 2 and 3
and another one:
I managed to solve question 6, 7, 8 and 9
vs
I managed to solve questions 6, 7, 8 and 9