Posted by **alyshan** on Wednesday, September 3, 2008 at 1:50pm.

a boat travels 12 km upstream and back in 1 hour and 45 min.if the speed of the current is 3 km/h throughout,find the speed of the boat in still water,giving your answer correct to 3 decimal place.

NOTE:(Answer is 14.3 km/h,so can any one show me the solution).

- mathematics -
**David Q**, Wednesday, September 3, 2008 at 5:12pm
The speed in still water is X km/h, so the speed upstream is (X-3) km/h (slower than X because it's upstream), and the speed downstream is (X+3) km/h (faster than X because it's downstream).

Travelling at (X-3) km/h for 12 km will take 12/(X-3) hours, and travelling back again at (X+3) km/h for 12 km will take another 12/(X+3) hours.

But the whole journey takes 1.75 hours, so 12/(X-3) + 12/(X+3) = 1.75 = 7/4. We need to solve this for X. After a bit of algebraic shuffling of the above terms, we end up with 7X²-96X-63=0. One of the two solutions of this is negative and therefore impossible; the other one should be the answer you're looking for.

## Answer This Question

## Related Questions

- math - A boat travels 8km upstream and back in 2 hours. If the current flows at ...
- Algebra - A fisherman traveled in a boat from point N upstream. After having ...
- Math - in still water, a speed boat travels 5 times faster than the current of ...
- Math - in still water, a speed boat travels 5 times faster than the current of ...
- MATH - In still water, a speed boat travels 5 times faster than the current of ...
- Intermediate Algebra Word Problem - A river's current is 4mph. A boat travels 48...
- UPSTREAM - THIS EXURSION WITH A BOAT TRAVEL 35KM UPSTREAM AND THEN BACK AGAIN IN...
- Math - How do you set this up? Solve the system using substitution: A boat ...
- Algebra - I am having a hard time with this question. A boat went 15 miles ...
- Algebra(urgent) - a boat moves through still wather at x kilometers(km) per hour...

More Related Questions