Answer:
4
Step-by-step explanation:
Given: total persons in IT department=60,23 people work on system security, 28 work on program implementation, and 26 work on platform development. 7 people work on system security and platform development, 12 people work on program implementation and platform development, and 6 people work on all three projects.
To Find: number of people working only on system security and program implementation.
Solution:
let people in system security be=
, 
let people in program implementation be=
, 
let people in platform development be=
, 
persons working in
and
=
∩
,
∩
=
persons working in
and
=
∩
,
∩
=
persons working in
and
=
∩
=
persons working in
,
and
=
∩
∩
,
∩
∩
=6
Now,
we know that
∪
∪
=
+
+
-
∩
-
∩
-
∩
+
∩
∩
on putting values,
60=23+28+26-7-12-
∩
+6
∩
=64-60
∩
=4
hence, the number of persons working in system security and program implementation are=4