Algebra help

Question

A boat travels 16 miles upstream and 15 miles downstream. The total time for both parts of the trip is 9 hours. The speed of the boat in still water is 9 mph. Find the speed of the current. 

Answer 1

let x be the speed of the current:

 

16 = (9 - x)t

 

t= 16/(9 - x)

 

substitute t into equation below:

 

15 = (9 + x)(9- t)   ----> -9x² -x + 450 use quadratic formula ---> [1 ± √[1 - 4*(-9)*450]]/2*(-9)

 

so x ≈ 7.016miles/hour

 

 

Answer 2

Hello again, Erica -- in still water, we could travel 81 miles in 9hr ... current is serious ...

8mph current takes 16hr up ... 7mph current takes 8hr up and 15mi/16mph ~1hr back ...

current is about 7mph  ... Best wishes, ma'am :)