In a class of 40 students, 5 like neither Nokia nor
Techno. 30 like Techno and Nokia. How many
students like only Nokia if altogether 35 like Techno?

The number of students that like only Nokia

Step-by-step explanation:

consider N the number of students who like Nokia → N=?

               T the number of students who like Techno → T=35

Statement 1: In a class of 40 students, 5 like neither Nokia nor Techno

we can translate it like this: 35 student like Nokia or Techno

we can note it like this : T∪N= 35

Statement 2: 30 like Techno and Nokia

we can note it : T∩N = 30

using a rule concerning the number of element of a set :

T∪N = N + T - T∩N

then

35 = N + 35 - 30

⇒ N - 30 = 0

⇒ N = 30