Answer
$(a)\space0.45 \\
(b) \space 0.75 \\
(c) \space0.9$
Work Step by Step
Use the formula for a probability $P$ as: $\text{Probability}=\dfrac{\text{Number of favourable outcomes}}{\text{Number of all outcomes}}$
We can see that these events are mutually exclusive, so we will evaluate the results by simply adding the individual probabilities.
(a) Probability for at most 2 people (which means $2$ or less):
=$P(0)+P(1)+P(2)=0.10+0.15+0.20=0.45$
(b) Probability for at least 2 people (which means $2$ or more):
=$P(2)+P(3)+P(\geq4)=0.20+0.24+0.31=0.75$
(c) Probability for at least 1 person (which means $1$ or more):
=$P(1)+P(2)+P(3)+P(\geq4)=0.15+0.20+0.24+0.31=0.9$
