请教一个概率问题，希望大家能给解释一下，谢谢谢谢

40% of students at the University of Toronto are registered to vote. 60% of
those registered to vote prefer candidate A and the remainder prefer Candidate B. 70% of those
not registered to vote prefer candidate B and the remainder prefer the candidate A.

47. What is the probability that a student chosen at random prefers the Candidate A?
A. 0.58
B. 0.42
C. 0.60
D. 0.48
E. 0.46

Solution: P=0.4*0.6+(1-0.4)*(1-0.7)=0.42

48. What is the probability that a student who prefers candidate B is registered to vote?
A. 0.580
B. 0.160
C. 0.267
D. 0.276
E. 0.367

Solution: P=(0.4*(1-0.6))/(0.4*(1-0.6)+(1-0.4)*0.7))=0.276

49. What is the probability that a student is either not registered or prefers candidate B?

A. 0.58
B. 0.68
C. 0.76
D. 0.70
E. 0.69

Solution: P=(1-0.4)+(0.4*(1-0.6)+(1-0.4)*0.7))-(1-0.4)*0.7=0.76

50. In a group of 10 registered voters what is the probability that between 2 and five voters prefer
candidate B?
A. 0.788
B. 0.667
C. 0.633
D. 0.452
E. 0.534

Solution: P=P(2)+P(3)+P(4)+P(5)

建议画个图就能够辅助解答了

（姑且把总人数设定为100）

50. In a group of 10 registered voters what is the probability that between 2 and five voters prefer
candidate B?
A. 0.788
B. 0.667
C. 0.633
D. 0.452
E. 0.534

Solution: P=P(2)+P(3)+P(4)+P(5)

不太理解这个…… 哪位大侠解释下哈！