Answer:
(a): 10 civil servants who were absent.
(b): 15 civil servants are in field only.
Step-by-step explanation:
Let;
[tex]{ \rm{ \sum(n) = 90}} \\ \\ { \rm{n(o) = 65}} \\ \\ { \rm{n(f) = 50}} \\ \\ { \rm{(o \: { \huge{n}} \: f) = 35}}[/tex]
Question (a):
Let the absentees be x
[tex]{ \rm{x + (65 - 35) + (50 - 35) + 35 = 90}} \\ \\ { \rm{x + 80 = 90}} \\ \\ { \rm{x = 10}}[/tex]
There are 10 absentees.
Question (b):
Servants in field only;
[tex]{ \rm{n(f \: only) = 50 - 35}} \\ \\ { \rm{n(f \: only) = 15 \: servants}}[/tex]