幾條數學題......20分......(請有心人幫幫手)

2008-07-22 12:16 am

1.It takes 30 minutes or less to walk from home to school and back home again when walking at 30m/min to school and walking at 45m/min from school. What is the distance between home and school?

2.Tom’s home is 1800m from his school. One morning he walked part of the way to school and then ran the rest. If it took him 20 minutes or less to get to school, and he walks at 70m/min and runs at 210m/min, how far did he run?

3.There are 200 notebooks to be handed out to the students of a class. If 30 of the students are given 4 each and the other are given 5 each, there will be some notebooks left over. However, there are not enough notebooks to give 20 of the students 4 each and the others 5 each. exactly how many students are there in the class?

回答 (1)

Ka Yan

2008-07-22 1:35 am

✔ 最佳答案

t : time
v : velocity
d : distance

(*因為冇 "細過及等於" 的符號, 所以於第1. & 2. 題用 "=" 代替之.)

1. t =30
t v =30(30 45)
d =2250m

2. t=20
70/(1800-d) 210/d=20
70d 210(1800-d)=20d(1800-d)
20d^2 -36140d 378000=0
d=10.52m~1796.48m

3. 4(30) 5x < 200
& 4(20) 5(10 x) > 200
;
;
x>14 & x<16
x = 15
There are (30 15)=45 students in the class.

2008-07-21 17:38:38 補充：
第3.題
There are (30+15)=45 students in the class. <--漏左個"+" 號.

參考: myself

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