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Home Q & A Board Science-Related Homework Help Mathematics
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10 years ago
Q: Two planes start from the same airport and fly in opposite directions. The second plane starts 0.5hour (30minutes) after the first plane, but its speed is 80 kilometers per hour faster. Find the airspeed of each plane if 2 hours after the firs plane departs  the planes are 3200 kilometers apart.

I have to solve this using linear equations with two variables. If I was to set up an equation, is it
3200=2(80+x) + 2y  ? If so, what would the other equation be?
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wrote...
#1
10 years ago
i would say y = 80 + x and 3200 = 1.5y + 2x.
so
3200 = 1.5(80+x) + 2x
Why 1.5? Because the first plane starts after half hour.
Now you solve the above eqution ang get the results for x and y. Have fun.
wrote...
#2
10 years ago
A couple of things:

1.  The two variables are the speed of the two aircraft, one of which is 80 greater than the other.  So one of your two equations is y= x + 80.
2.  The second equation would be 3200 = 1.5y + 2x.  You have it as both planes have been in the air for 2 hours; they have not.  One has only been up for 1.5 hours.

So your equations are:
y = x + 80
1.5y + 2x = 3200

Substitute x + 80 in for y in the second equation and solve for x (you should get 880 for x), then plug that back into the first equation to get y (960).  Thus the first plane will have flown 1760 km away from the airport and the second one will be 1440 km away, which gives you your 3200.
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tom_vantom_van
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#3
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10 years ago
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#4
10 years ago
3200=1,5(x+80) +2x
x=880
1-st plane - 1760
2-nd plane - 1440
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