问题 解答题

对某种产品的6件不同正品和4件不同次品一一进行测试,至区分出所有次品为止.若所有次品恰好在第5次测试时被全部发现,则这样的测试方法有多少种可能?

答案

第5次必测出一次品,余下3件在前4次被测出,从4件中确定最后一件品有C41种方法;

前4次中应有1正品、3次品,有C61C33种,

前4次测试中的顺序有A44种,

由分步计数原理得这样的测试方法有C41(C61C33)A44=576种可能.

单项选择题

"I was just like you--I’ thought I was invincible," says Adam Blomberg, standing before 400 students in a darkened auditorium at Miami’s Coral Reef Senior High School. A photo of a bloodied and unconscious teenager, a breathing tube protruding from his mouth, flashes on the wall.

"That was me," he says. There’s a collective gasp before the room grows silent and Blomberg,31, an anesthesiologist who trained at Brigham and Women’s Hospital in Boston, begins the story of what happened one night in February 1995.

He created a presentation illustrating the dangers of behaving irresponsibly in a car, from not buckling up to speeding to driving under the influence of alcohol and drugs. He tracked down photos of teen crash victims from the center’s archives, then incorporated statistics and his own experience. He spoke the first time to a local Boy Scout troop and was soon giving his talk, "A Survivor’s Story," at high schools around the state.

The Blomberg family had reason to celebrate. Adam had fully recovered and was on his way to fulfilling his lifelong dream of becoming a doctor. But in January 2000, Blomberg’s 22-year-old step-brother, Michael, was killed in a crash while driving to his Atlanta home late one night. He wasn’t wearing a seat belt. After the accident, Blomberg stopped telling his story to crowds, racked with guilt over his inability to reach Michael. If Blomberg had failed his own brother, he reasoned, how could he possibly make a difference to a roomful of strangers Requests from schools continued to roll in, but he turned down every one.

Then Blomberg got a call from a high school counselor. As he started into his standard excuse-lack of time—he looked across the room at a stack of thank-you notes from students who had heard him speak. He realized that kids needed to hear what he had to say. He agreed to visit the school and began contacting others on the waiting list for his talks.

Blomberg leaves the school hoping he has changed someone’s behavior. He recalls a letter he received from a student who heard him speak and got into a crash later that same day but was unharmed. " She told me she was wearing her seat belt because of me."

Letters like this reinforce his belief that he survived the accident for a reason. "There are a lot of physicians in the world, and we all save lives," he says. "I have a special opportunity to save lives not just as a doctor but also as a human being.\

Which one of the following is the best title for this passage()

A. Teen Driving Risks Are Highest

B. Vehicle Safety Trends Will Drive Interior

C. Road Safety Management and Emergency Response

D. Teaching Teens Safe Driving

判断题