How do I do this? The Steps please.

Question

On the Snake River, Jim can row 30 km downstream in the same amount of time he can row 18 km upstream. The rate of the current is 2km/h. Find the rate Jim can row.

Answer 1

Use the dimensions to tell you how to set up the problem.  You are given an equality between two periods of time in hours.

 

hrs = hrs

 

you are provided two distances in miles, and you are asked to calculate miles per hr.

 

miles/(miles/hr) = hours

 

you are solving for Jim's rowing speed which is x in mi/hr.

 

when he is swimming upstream, his net speed is (x-2) mi/hr.

when he is swimming downstream, his net speed is (x+2) mi/hr.

 

his time swimming downstream is (30 mi)/(x+2)mph = 30/(x+2) hrs.

his time swimming up stream is (18mi)/(x-2)mph = 18/(x-2)  hrs.

 

30/(x+2) = 18/(x-2)

30x - 60 = 18x + 36

12x = 96

x = 8

 x is defined in mph, so

 

Jim's swimming speed is 8 miles/hour.