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# WORD PROBLEM HELP!!!

The curren in a stream moves at a speed of 4 mph. A boat travels 5 mi upstream and 13 mi downstream in total time of 2 hr. What is the speed of the boat in still wanter??

here is the second one. I don't even know where to start on this one.

A tablecloth measures 96in by 72in. It is laid on a tabletop with an area of 5040in2, and hangs over the edge by the same amount on all sides. By how many inches does the cloth hang over the edge??

### 1 Answer by Expert Tutors

Robert J. | Certified High School AP Calculus and Physics TeacherCertified High School AP Calculus and Ph...
4.6 4.6 (13 lesson ratings) (13)
2

1) Let u = the speed of the boat in still water. So, the speed in upstream is u-4, and the speed in downstream is u+4.

Balance by the total time,

5/(u-4) + 13/(u+4) = 2

Multiply both sides by (u-4)(u+4),

5(u+4) + 13(u-4) = 2(u2 - 16)

Simplify,

u2 - 9u = 0

Since u can not be zero, divide both sides by u and solve for u,

2) Let x be the length hanging over the edge.

(96-2x)(72-2x) = 5040

/4, (x-48)(x-36) = 1260

x2 - 84x + 468 = 0

(x-6)(x-78) = 0

Attn: x = 78 is not a solution.

Simplify,

u2 - 9u = 0

This is where I was messing up? How did you get that?

Use the units.  miles/mph = hours

hours going upstream + hours going downstream = 2

5(u+4) + 13(u-4) = 2(u2 - 16)

5u+20+13u-52 = 2u2 - 32