Question

In a survey of 300 android mobile users, who make video calls, 75 people said they use viber, 45 use skype and 90 people use both. The number of persons who use neither viber nor skype is :-

Answer 1

let people use viber be a and people use skype be b.
total mobile users =N(u)=300
N(a)=75,N(b)=45,N(a&b)=90
Total no. of people who uses viber or skype N(a orb)= N(a)+N(b)-N(a&b)
=75+45-90
=120-90
=30
The number of persons who use neither viber nor skype =N(u)-N(a orb)
=300-30
=270