math
posted by Lauren .
Erin takes a total of 5 hours in her boat to travel a distance upriver and return downriver the same distance. If the time traveling upriver is twice the time traveling downriver, how many hours does each trip take?
How do I put this into two equation and use the matrix to solve it?

u = 2d
or
u  2d = 0
u + d = 5
so the matrix would be
1 2 0
1 1 5
add 1 times the 1st row to the 2nd row. Then you get
1 2 0
0 3 5
multiply the 2nd row by 1/3:
1 2 0
0 1 5/3
The 2nd row tells us that d = 5/3, so u = 10/3 
I don't know about the matrix, but it is not necessary to solve the problem.
x = time traveling down river
2x = time traveling up river.
x + 2x = 5
3x = 5
x = 5/3 hour = 1 hour, 40 minutes
2x = ?
I hope this helps.
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