Need Help with Algebra/ Equations again!!
By jennybianca
@jennybianca (12912)
Australia
May 11, 2008 4:29am CST
I know this is the second time I have posted a question for help with my daughters algebra.
The person who responded was brilliant. However I can't be certain of obtaining help quickly from the same person, so I am posting the question here.
We would be very grateful for help.
Here are the two problems:
1)
A school is expected to plant trees along a river bank. The project is to take a certain number of days.
If they plant 240 trees per day, then they will be short by 400 trees.
If they plant 280 trees per day, they will plant 200 more than planned.
How many trees are planted, and how many days will it take?
2)A train passes a pole in 15 seconds, and in 45 seconds it passes through a tunnel 600 metres long. What is the speed of the train? How long is it?
2 responses
@subashmanchanda (26)
• India
14 Jan 10
Jennybianca Ji,
Hello! The answer to your first question is that the number of days given are: 15 and the trees to be planted are 4000. Just assume the no. of days = X. The equation would be 240X = 400 = 280X - 200. By this way, the number of days would come to 15. Then put the value in any of the equation, and the no. of trees you get as 4,000.
The answer to your second question is that the speed of the train is 48 Km/per hour and the length of the train is 200 metres. The tunnel being 600 metres and the time covered is 45 seconds, so in 15 seconds the train would cover only 200 metres that is the time taken to cross the pole. Thus, the length of the train is 200 metres. And now the speed 15 seconds = 200 metres or 15 seconds = 200/1000 Km then 3,600 seconds = 200/1000 x 3600/15 = 48 Km. per hour.
1 person likes this
@jennybianca (12912)
• Australia
14 Jan 10
Wow! This is fantastic. Thanks very much. My daughter will be grateful.
@smacksman (6053)
•
11 May 08
And the answer to the second one:-
What is the speed? The answer will be in metre/second which is the modern metric way of saying miles per hour. And in maths '/' or 'per' means divide.
So 600metres/45seconds = 13.33m/s
How long is the train? Well we have to be a bit smartypants and assume from the question that the train is going at a constant speed, the same as going through the tunnel.
If the train takes 45s to go 600m and and we know that 15s is a third of 45s (15/45 = 1/3) then the train is a third of 600m so = 200m
@jennybianca (12912)
• Australia
12 May 08
I showed my daughter your response, & it helped her greatly. Thank you very much.
