生产工艺工程中产品的尺寸误差X(mm)～N(0,1.52),如果产品的尺寸与规定_爱下问搜题

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问题解答题

生产工艺工程中产品的尺寸误差X(mm)～N(0,1.5²),如果产品的尺寸与规定的尺寸偏差的绝对值不超过1.5mm为合格品，求（1）X的密度函数；（2）生产的5件产品的合格率不小于80％的概率.

答案

见解析

解：（1）由题意知X～N(0,1.5²),即

所以密度函数；

（2）设Y表示5件产品中的合格品数，每件产品是合格品的概率为

P(|X|≤1.5)=P(-1.5<X≤1.5)=0.6826

而Y～B(5,0.6826),合格率不小于80％，即Y≥5×0.8=4

所以P(Y≥4)=P(Y=4)+P(Y=5)==0.4927

完形填空

By my third day in the hospital, I realized Tom didn’t visit. I couldn’t understand 36 my best friend wouldn’t come to see me. Struggling against the 37 , I phoned his __38 . His mother answered, and when I asked for Tom, she got 39 . “He’s not here right now,” she said. I thought it was 40 that she didn’t tell me where he was or 41 to have him call me. But I was so weak, I just let it 42 . I found out later that Tom’s mother called my parents right after we rang 43 . My phone call really made her 44 , and she 45 they talk to me. Later that night, my mom 46 . Did I remember drinking? Did I remember in a car？I had 47 what she was talking about, so she finally told me the news: I’d hit a tree. Tom, in the 48 seat, was thrown from the car and killed instantly. The only reason I’d lived was because of my 49 .
My first 50 was of shock. I’d been drink-driving? Hit a tree? Killed Tom? I felt like the 51 person in the world. Even after I was able to 52 several weeks later, I didn’t want to eat, I didn’t want to talk. I just 53 at the wall in my 54 and cried. The only person I wanted to see was Tom. I didn’t feel like 55 with any of my old friends.

D．unnecessary

A．disappointed

C．called back

D．most lonely

C．setting out

D．hanging out

单项选择题

可促进胆囊收缩和胰酶分泌的胃肠激素是（）

A．促胃液素

B．缩胆囊素

C．促胰液素

D．抑胃肽