rate and ratio

(1)
(a)
Speed of the rabbit
= (760 m)/(80 s)
= 9.5 m/s

Speed of the dog
= (522 m)/(60 s)
= 8.7 m/s

(b)
Since 9.5 m/s > 8.7 m/s,
the rabbit runsfasterthan the dog.


=====
(2)
(a)
Speed of the van
= (36 km)/(0.5 h)
= 72 km/h

(b)
Distance travelled in 20 minutes
= (72 km/h) x (20/60 h)
= 24 km


=====
(3)
7a - 3b = 5a
7a - 5a = 3b
2a = 3b
a/b = 3/2
a : b = 3 : 2


=====
(4)
a : b = 5 : 9
b : c = 3 : 2 = 3x3 : 2x3 = 9 : 6

a : b : c = 5 : 9 : 6

1a. The speed of the rabbit
=760m/80s
=9.5 m/s
The speed of the dog
=522m/1minutes
=522/60s------------------change it to the same unit as the speed of rabbits
that that's easier to compare
=8.7 m/s
1b. Since 9.5m/s > 8.7m/s
So the rabbit ran faster than the dog.

2a. The speed of the van
=36km/0.5hr
=72 km/hr

2b. The distance required
=72*(20/60)----------Since 60 mins is an hr...So 20 mins=20/60 hr(i.e. 1/3 hr)
=24 km

3. 7a-3b=5a
7a-5a=3b-----------將a的group埋一齊...b的又group....搵出幾多a是3b
2a=3b
a/b=3/2-----------將除號化做':'
So a:b is 3:2

4. a:b =5:9 =5*3:9*3
b:c= 3:2= 3*9:2*9
a:b:c= 15:27:18

Tips:我地知道b係兩個不同比例中的數值...所以可以搵兩個b的公倍數...然後將a同c乘番一樣比例


2012-03-14 21:58:52 補充：
correction: 第4題應該係咁...
a:b=5:9=5*1:9*1
b:c=3:2= 3*3:2*3
a:b:c=5:9:6

乘3比乘9更方便..所以應該*3