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#1 2007-01-21 08:03:07
- Akila.B
- Member
- Registered: 2007-01-14
- Posts: 3
Math
Hi,
Can anyone help me to solve these problems? I need steps.
1. 1.If the total distance of a journey is 120 km.If one goes by 60 km/hr and comes back at 40km/hr what is the average speed during the journey?
2.1.City A's population is 68000, decreasing at a rate of 80 people per year. City B having population 42000 is increasing at a rate of 120 people per year. In how many years both the cities will have the same population?:)
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#2 2007-01-21 08:26:42
- Devantè
- Real Member
- Registered: 2006-07-14
- Posts: 6,400
Re: Math
This belongs in -------------------> Help Me! [ section ].
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#3 2007-01-21 09:22:46
- MathsIsFun
- Administrator
- Registered: 2005-01-21
- Posts: 7,711
Re: Math
Moved 
Speed is distance/time. So let us work out the total distance and the total time.
Total distance is already given: 120 km (I assume that is what they mean ... that each direction was 60 km and the total is 120 km)
Total Time is made up of the time out, and the time back.
Time Out = 1 hr (60 km at 60 km/h takes one hour)
Time back = 60 km / 40 km/h = 1.5 h
Total Time = 1+1.5 = 2.5 h
So speed for the total journey = 120 km / 2.5 h = 48 km/h
(Interesting Point: it does not matter how far, so long as the distance out and back are the same.)
"The physicists defer only to mathematicians, and the mathematicians defer only to God ..." - Leon M. Lederman
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#4 2007-01-21 10:08:47
- mathsyperson
- Moderator
- Registered: 2005-06-22
- Posts: 4,900
Re: Math
2)
City A's population decreases by 80 people per year, and City B's population increases by 120 per year, so overall City B gets 200 more people than City A every year.
Right now, A has 16000 more than B, and so for B to catch up with A will take 16000/200 = 80 years.
Incidentally, Devanté, you don't have to wait for a topic to be moved before helping.
Edit: See pi man's post below. I've left the error in my post so that his makes sense, but don't copy it!
Why did the vector cross the road?
It wanted to be normal.
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#5 2007-01-21 11:48:06
- pi man
- Member
- Registered: 2006-07-06
- Posts: 251
Re: Math
One small correction to Mathsyperson response. The difference between the two populations is 26000, not 16000. So add on another 50 years. 26000/200=130.
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