问题 解答题

通讯中,发报方常采取重复发送同一信号的办法来减少在接收中可能发生的错误,.假定发报机只发0和1两种信号,接收时发生错误的情况是:“发0收到1”或“发1收到0”,它们发生的概率都是0.05.

(Ⅰ)若一个信号连续发2次,接收时“两次信号相同”,接收方接收信号;否则不接收,则接收方接收一个信号的概率是多少?

(Ⅱ)若一个信号连续发3次,按“少数服从多数”的原则接收,则正确接收一个信号的概率是多少?

答案

(Ⅰ)正确接收一个信号的概率为

(1-0.05)×(1-0.05)=0.9025

错误接收一个信号的概率为0.9025+0.0025=0.905

(Ⅱ)考虑对立事件,错误接收一个信号的概率为

23×0.052×0.95+33×0.053=0.00725

∴正确接收一个信号的概率为1-0.00725=0.99275

阅读理解

One day while shopping in a small town in southern California,it was my misfortune to be approached by a clerk whose personality conflicted with mine. He seemed most unfriendly and not at all concerned about my intended purchase. I bought nothing,and marched angrily out of the store. My hostility(敌意) toward that clerk increased with each step.

On the outside,standing by the road,was a dark­skinned young man in his early twenties. His expressive brown eyes met and held mine,and in the next instant a beautiful, dazzling smile covered his face. I gave way immediately. The magnetic(磁力的) power of that smile dissolved all bitterness within me,and I found the muscles in my own face happily responding(回应).

“Beautiful day,isn't it?”I remarked,in passing. Then,I turned back.“I really owe you a debt of gratitude,”I said softly.

His smile deepened, but he made no attempt to answer.A Mexican woman and two men were standing nearby.The woman stepped forward and volunteered, "Sir, but he doesn't speak English.Do you want me to tell him something?" In that moment I felt transformed(改变).The young man's smile had made a big person of me.My friendliness and good will toward all mankind stood ten feet tall.

"Thank you?" The woman seemed slightly puzzled.

I gave her arm a friendly pat as I turned to leave."Just tell him that," I insisted."He'll understand.I am sure !"

Oh, what a smile can do! Although I have never seen that young man again, I shall never forget the lesson he taught me that morning.From that day on, I became smile-conscious, and I practice the art anywhere and everywhere, with everybody.

小题1:Why did the author leave the store angrily?

A.The clerk treated him unkindly.

B.He couldn't buy what he wanted.

C.The clerk didn't speak English.

D.The store's goods were too dear.小题2:By saying "I felt the muscles(肌肉) in my own face happily responding" (in Paragraph 2), the author means __.

A.he was still angry

B.he did not want to smile

C.he would thank the young man

D.he smiled back at the young man小题3:The author asked the woman to say "Thank you!" to the young man because the young man_____.

A.had helped the author before

B.taught the author how to smile

C.was a kind employee of the store

D.taught the author a valuable lesson小题4:In the passage, the author seems to suggest that we should __   ___.

A.be generous to strangers

B.practice smiling every day

C.smile at other people

D.help people in trouble

问答题 简答题