In a group of 40 people, 16 owned at least a phone, 7 owned only a tablet and it's known 13 owned both. What's the probability that a person, picked at random, owned neither?

40 people in total16 = at least a phone, 7 = only a tablet, 13 = both
Must figure out how many people just own a phone: 16 - 13 (both phones and tablet) = 3 (just own a phone)
So, can construct a Venn diagram to show that, of the entire group of 40, those who own either a phone or tablet break down into these categories: 3 people own only phones, 13 own both a phone and tablet, 7 own only a tablet.
3 + 13 + 7 = 23 (own a phone and/or a tablet)
Subtract this number from the total size of the group to find number of people who don't own either:40 - 23 = 17 (don't own either)
Answer:17/40