maths (quickly)

2007-06-04 4:50 am

1) 1/2 : 7=5 : a = 2b : 56
find the two unknown

2)the population of a town was 5 000 000 which included 875000 newborn babies. What was the birth rate in births per 1 00 people?

3)the temperature of water in an electric boiler is raised from 25℃to 100℃ in 15 minutes. what is the rate of temperature rise in ℃per mimute?

更新1:

need to step!!!

更新2:

re : 1) What was the birth rate in births per 1 000 people?

回答 (4)

toyszchun

2007-06-04 5:05 am

✔ 最佳答案

1)
1/2 : 7=5 : a
0.5 ÷ 7 = 5 ÷ a
a = 7×5÷.5
a = 70

1/2 : 7 = 2b : 56
0.5÷7 = b÷28
b= 2

2)
birth rate
=875000÷5 000 000×100
=875÷5 0
=17.5 per 1 00 people

3)
rate of temperature rise
=(100-25)÷15
=5℃per mimute

👍 0 👎 0

小艾美

2007-06-04 5:27 am

1) 1/2 : 7=5 : a = 2b : 56
1/2 : 7=5 : a
0.5:7=5:a
0.5a=7(5)
a=7(5)/0.5
a=70
5 : a = 2b : 56
5:70=2b:56
70(2b)=56(5)
140b=56(5)
b=56(5)/140
b=2
2)newborn babies/100=875000/5000000
875000/5000000*100=1.75
The rate is100:1.75.
======
3)25/15= 2
1---
3

👍 0 👎 0

shuryanc

2007-06-04 5:10 am

1)
1/2:7=5 : a = 2b : 56
(1/2)/7=5/a=2b/56
so (1/2)/7=5/a
a/14=5
a=70
so 2b/56=5
b=140

2)唔係太明(the birth rate in births per 1 00 people)
3)
(100℃-25℃)/15
=5℃/mins

👍 0 👎 0

志仁

2007-06-04 5:03 am

1)

1/2 : 7=5 : a = 2b : 56

0.5:7=5:a
5:70=5:a -----------(0.5 x 10:7 x 10)
a=70

0.5:7=2b:56 -----------(0.5 x 8:7 x 8)
4:56=2b:56
b=4

2) 875000/5000000 x 100
= 17.5 per 100 people

3) (100-25)/15
=75/15
=5℃per mimute

👍 0 👎 0

收錄日期: 2021-04-23 17:01:00
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20070603000051KK04751

檢視 Wayback Machine 備份