1.)In a test, the average mark of a group of 50 students is 83.2.If the average mark of the boys is 86,while that of the girls is 81,find the number of boys in this group.
2.)Jack can ride from town X to town Y and back in a certain time at a speed of 10 km/h. If he were to ride from town X to town Y at 9km/h,and return at 12km/h,he would save 15 minutes.Find the distance between the two towns.
Mahs questions???(2)
2006-11-26 7:33 pm
回答 (1)
2006-11-26 8:06 pm
✔ 最佳答案
1) Let b be the no. of boys in this group[ 86 x b +81 x (50-b) ] / 50 = 83.2
x=22
2) Let s be the distance between two towns
(9 x s + 12 x s) - 10 x 2 x s = 1/4 [convert minutes into hours]
s=0.25 km
3) From the given information,
d+67=a --- (1)
2d=e --- (2)
a+b+c+d+e = 540
As we know that a=c & b=e
2a+2e+d = 540
From (1) & (2),
2(d+67) + 2(2d) + d =540
d=58
Therefore, a=c=58+67=125
b=e=2x58=116
Hope these can help u
收錄日期: 2021-04-11 16:26:11
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20061126000051KK01551