帮忙解3个数学题，谢谢了。

来源：百度知道 编辑：UC知道 时间：2024/06/22 15:18:02
1.A plumber charges a basic service fee plus a labor charge for each hour of service.A 2-hour job costs $120 and a 4-hour job costs $180.Find the plumber's basic service fee.
2.Jerry has received the following math test scores:80,75,79,86.His final exam is worth 200 points and counts as two tests.What is the lowest score he can get to keep an average of at least 80 points?
3.A Native American art museum charges $8 per visit to nonmembers.Members pay a $40 membership fee and get in for a reduced rate of$5.How many times must a person visit the museum for membership to be less expensive than paying for each visit as a nonmember?
都要过程就好~谢谢亲们！！

My Solutions:
1. Let the basic service fee be X and labour charge for each hour be Y.
2X+Y=120
4X+Y=180
Solve them simultaneously,
we have X=30 and Y=60
Hence, the plumber's basic service fee is $60.

2.Let the lowest score he can get ... be X
80+75+79+86+X=80*6
X=160
Hence, the lowest score he ... is 160

3.Let the number of visits be X
40+5X＜8X
40＜3X
X＞13.3
Hence, the least number of visits the person should visit in order...is 14.

1. the first 2-hour job cost including basic fee and two hours charge, which is 120. If he works another 2 hours, then what he needs to be payed more is only 2 hours charge, which is 180-120=60, this means his labor charge for each hour is 30. so his basic fee is 120-2*30=60.

2. his first 4 tests average is (80+75+79+86)/4=80. so these 4 tests average is already 80 points. If his final exam score, which counts 2 tests, is 160, then he can keep an av