(急)想問以下呢d數學題點做也?

2012-01-31 9:02 am

如題拉~
呢d數全部都係比和率黎咖
有冇人識答也,雖然係英文= =
因為我要趕住交hw阿..
P.S答既時候記住列詳細步驟也.thz:)
1.Johnny drives a motorcycle at 90km/h for 40 minutes and then 70km/h for 1 hour and 8 minutes.Find his average speed for the whole journey.2.On a map of scale 1:5000,the length of a coastline is 12cm and the area of a garden is 30c㎡.Find
a.the actual length of the coastline in km
b.the actual area of the garden in k㎡3.Given that 3a=4b=2c.Find
a.Find a:b:c
b.Find b if a+b-c=34.Loretta got a few coins in the ratio 50-cent coins:20-cent coins:10-cent coins=7:4:6.The total amount of the coins is $9.8.Find the number of 50-cent coins she had.5.A construction project involves 12 engineers,8 clerks and 60 workmen.The monthly salary per staff of the three occupations are in the ratio 6:2:1.If the monthly salary of a clerk is$10000,find
a.the monthly salary of
I.an engineer
II.a workman,and
b.the average monthly salary for the 80 staff.

更新1:

仲有呢d... 6.The volumes of two metal spheres are in the ratio 8:64.If 64kg of paint are required to paint the surface of the larger sphere,find the weight of the paint required to paint the surface of the smaller sphere.

更新2:

7.A car takes 40 minutes to travel from Town A to Town B,and another car takes50 minutes to cover the same distance.If both cars start from Town A and Town B respectively at the same time,travelling towards each other,after how many minutes will they pass each other?

更新3:

8.One pipe can fill up a swimming pool in 5 hours,while another pipe can fill up the same pool in 4 hours.After the first pipe has already started filling the swimming pool for 1 hour,the second pipe starts.How long will it take to fill up the pool since the second pipe has started?

更新4:

9.The ratio of the present agesof Camille and her brother is 5:1.After two years, the ratio will be 3:Camille claims that the ratio becomes2:1 when she is 20years old.Is the claim correct?Explain ypur answer.

更新5:

10.Three construction teams,A,B and C,can complete a cotstruction project alone in 8,10 and 16 day respectively.They now work together to complete the project.The time each of them will spend is in the ratio of 2:3:4. a.How long does each team work?

更新6:

b.Find the time to complete the construction project if the three teams I.work simultaneously II.work one by one.

更新7:

tre****** : sor. 第9題係3:1~

回答 (1)

Trevor

2012-01-31 6:04 pm

✔ 最佳答案

1) (90*40/60+70*68/60)/(40+68)
= (600+79+1/3)/108
= 6+47/162
2) a) 12*5000/100000(in km)
= 0.6(km)
b) 30*5000/10000000000(in km^2)
= 0.000015(km^2)
3) a)3a=4b
4b=2c
a:b=4:3
b:c=1:2=3:6
a:b:c=4:3:6
Alternative Method
3*4=4*3=2*6
a:b:c=4:3:6 (by myself, it is a much quicker method)
b) Let a=4k, then b=3k,c=6k
a+b+c = 3
(4+3+6)k=3
13k =3
k=3/13
a=4*3/13=12/13
b=3*3/13=9/13
c=6*3/13=18/13=1+5/13
4) 7k:4k:6k
But their values are not in this ratio, it's only the amount of coins, so,
7(5)k:4(2)k:6(1)k
35k+8k+6k=98(since we mutiply with 毫子)
49k =98
k=2
7k(the amount of50cent coin)=7*2=14
5) a) I) 2k=10000
6k=30000(dollars)
II) 2k=10000
k=5000(dollars)
b)(12*30000+8*10000+60*5000)/80
= 5000/80(12*6+8*2+60*1)
= 62.5(148)
= 9250 (dollars)
6) smaller one is 1k (after simplify)
larger one is 8k (after simplify)
larger one now is 8k+64
because it is painted.
8k+64=8(k+8)
(k+8):8(k+8) may be changed into 8:64
Then 8kg paint is required to paint on the surface of the smaller sphere.
7) Let the distance between Town A and Town B is x
Then Car A's speed is x km/40 mins
Same, Car B's speed is x km/50 mins
x/(x/40+x/50)(since the cars is going towards each other, their speed they spent is their sum of speed)
= x/(9x/200)
= x(9/200x)
= 200/9 (minutes)
8) Same as 7), Pipe A is x/5, Pipe B is x/4
4x/5(when the first pipe open for one hour, the capacity of the swimming pool)/(x/5+x/4)
= 4x/5 /(9x/20)
= 4/5/9*20
= 16/9(hours)
9)3:what?
I will do it for you but you have to check what ' what 'the number is!
Same as 5) and 6) , 5k:1k (present ages)
5k+2: k+2(Is that 3:1)
If yes, please look at the following.
5k+2=3(k+2)
5k+2=3k+6
2k=4
k=2
5k+18:k+18= 28:20(not 2:1)==
10)a)Same as 5)6)8) A's speed is x/8, B's speed is x/10, C's speed is x/16
kx/4+3kx/10+kx/4=x
4kx/5=x
k=5/4
A=2*5/4=5/2(days)
B=3*5/4=15/4(days)
C=4*5/4=5(days)
b)II)Like a)
5/2+15/4+5=45/4(days)
b)I) 5days, since it is the longest time to work among three teams.
Hope can help you.

參考: all by myself

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