In a survey of 420 people, 230 use samsung mobile, 180 use iphone, 90 use both ,find the number of p

[math_celebrity]

In a survey of 420 people, 230 use samsung mobile, 180 use iphone, 90 use both ,find the number of people who don't use either of them

People who don't use both is:
420 - (230 + 180 - 90)
420 - (320)
100