Question

A motorboat travels 244 kilometers in 4 hours going upstream and 749 kilometers in 7 hours going downstream. What is the rate of the boat in still water and what is the rate of the current

Answer 1

Answer:

Speed of Motorboat = 84 kmph

Speed of Current = 23 kmph

Step-by-step explanation:

Distance Equation is:

D = RT

Where

D is distance

R is rate

T is time

Downstream rate is rate of boat PLUS current

Upstream rate is rate of boat MINUS current

Let rate of boat be "x" and rate of current be "c".

From first statement, we can write:

244 = (x - c)(4)

From second statement, we can write:

749 = (x + c)(7)

The first equation becomes:

244 = 4x - 4c

The second equation becomes:

749 = 7x + 7c

Multiplying first equation by 7 , we have:

7 * [244 = 4x - 4c] = 1708 = 28x - 28c

Multiplying 2nd equation by 4, we have:

4 * [749 = 7x + 7c] = 2996 = 28x + 28c

Now we add up these equations (in bold):

1708 = 28x - 28c

2996 = 28x + 28c

----------------------------

4704 = 56x

x = 4704/56

x = 84

Now using this value and plugging in original equation, we can find "c":

244 = 4x - 4c

244 = 4(84) - 4c

244 = 336 - 4c

4c = 92

c = 92/4

c = 23

Speed of Motorboat = 84 kmph

Speed of Current = 23 kmph