Which equations show that the set of whole numbers is not closed under subtraction?

choose all answers that are correct.

a.
1 – (–2) = 3

b.
1 – 2 = –1

c.
2 – 0 = 2

d.
2 – 4 = –2

An office supply company conducted a survey before marketing a new paper shredder designed for home use. in the survey, 80 % of the people who tried the shredder were satisfied with it. because of this high satisfaction rate, the company decided to market the new shredder. assume that 80 % of all people are satisfied with this shredder. during a certain month, 100 customers bought this shredder. find the probability that of these 100 customers, the number who are satisfied is 69 or fewer.