问题 解答题
学校食堂改建一个开水房,计划用电炉或煤炭烧水,但用煤时也要用电鼓风及时排气,用煤烧开水每吨开水费用为S元,用电炉烧开水每吨开水费用为P元,S=5y+0.2x+5,P=10.2x+20
76-x
,其中y为每吨煤的价格,x为每百度电的价格.如果烧煤时的费用不超过用电炉时的费用,则仍用原备的锅炉烧水,否则就用电炉烧水.
(1)如果两种方法烧水费用相同,试将每吨煤的价格y表示为每百度电价x的函数;
(2)如果每百度电价不低于60元,则用煤烧时每吨煤的最高价是多少?
答案

(1)若两种方法烧水费用相同,即S=P,

5y+0.2x+5=10.2x+20

76-x
…(2分)

y=2x+4

76-x
-1,0<x≤76…(4分)

(定义域不写或写错,扣1分)

(2)当x≥60时,60≤x≤76   …(6分)

76-x
=t,则0≤t≤4…(8分)

由题意知,y≤2(76-t2)+4t-1=-2(t-1)2+153…(10分)

(写y=2(76-t2)+4t-1=-2(t-1)2+153,扣1分)

当t=1即x=75时,ymax=153.   …(12分)

答:用煤烧时每吨煤的最高价是153元.…(14分)(不答扣2分)

阅读理解

阅读理解

     In Britain, in a population of 60 million, there are 13 million grandparents, many of whom live alone a

long way from their grandchildren.The loneliness of these older people has become an issue that schools

are trying to teach children about .

     On a popular teacher's website, there is a classroom activity to help make children aware of the

implications of the different generations of the same family living far from each other. It's a story about Mrs. Eiderdown, an elderly lady whose grandchildren have moved to Australia with their parents. She lives

alone and rarely sees her family .

     First of all, the children speculate about Mrs. Eiderdown's life.  What does she have for breakfast ?

what does she do all day ?how does she feel about her life ?

     One day, Mrs. Eiderdown decides that she wants a pet to keep her company and puts an

advertisement in a local shop window. Then she waits at home to see if anyone will answer her

advertisement .

     A tall thin man rings her doorbell. he is holding a cardboard box. Mrs. Eiderdown chats with the man

for ten minutes before she realizes that she hasn't looked in-side the box to see what the pet is. She can hear a his-sing sound. The children guess what is in the box(a snake). Mrs. Eiderdown thanks the man but

says she doesn't think the snake is a good idea .

     The next time the doorbell rings, there's a lady on the doorstep, also carrying a cardboard box.In the

bottom of the box, Mrs. Eiderdown sees something black and hairy with eight legs. Again ,the children say what they  think it is (a spider). Mrs. Eiderdown thanks the lady for her kindness but says that a spider is

not the sort of pet she has in mind.

At last, the little girl next door brings her a dog .Mrs. Eiderdown's life improves a lot because of the dog.

more importantly, of course, the little girl, whose own granny lives a long way away, starts to visit

Mrs.Eiderdown more often. This interactive classroom idea has led to a greater awareness among children about the possible loneliness of older people who live quite near them .

1.what's the main idea of the passage?

A.children get to know about the trouble of the elderly

B. neighbors help select pets for Mrs. Eiderdown

C. society helps the lonely people in the UK

D. school send pets to the lonely elderly

2.what does the underlined sentence in the third paragraph mean ?

A. they talk about how she feels about being old

B. they try to experience her loneliness

C. they try to imagine how she lives

D. they write about her life story

3.  what can we infer from the passage ?

A. the little girl often visits her own granny

B. the people who offer pets are lady's neighbors

C. the farther the elderly live ,the lonelier they feel

D. the little girl begins to care more about Mrs. Eiderdown

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