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1. It took a boat 2 hours to reach town A going upstream. The way back was 1 hour and 20 mins. What is the speed of the boat in still water if the speed of the stream is 3 mph?

 

2. It took a plane 2 hours to go from Dallas to New York with the head wind and 1.5 hours to get back with tail wind. If the speed of the wind was 30 mph, how far apart are two cities?

 
joebob  Nov 12, 2017
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1. Let the speed of the boat in still water=S
Distance =Speed x Time
2[S - 3] =4/3[S + 3], solve for S

 

2 (S - 3) = (4 (S + 3))/3

Multiply both sides by 3:
3×2 (S - 3) = (3×4 (S + 3))/3

(3×4 (S + 3))/3 = 3/3×4 (S + 3) = 4 (S + 3):
3×2 (S - 3) = 4 (S + 3)
6 (S - 3) = 4 (S + 3)
6 S - 18 = 4 S + 12​
S = 15 mph - The speed of the boat in still water.


2. Let the speed of the plane =S

Distance = Speed x Time

2[S - 30] =1.5[S + 30], solve for S

S = 210 mph [Use exactly the same procedure as in question 1.

2[210 - 30] = 2 x 180 =360 miles - the distance between Dallas and New York !!!!!!!!!!!!!!!!!!!!!.

Note: Given the numbers in your question, the solution is UNREALISTIC !!, since the ACTUAL distance between Dallas and New York City is an average of 1,378 miles and takes about 3 - 3 1/2 hours to fly from one to the other!!.

 
Guest Nov 12, 2017

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