Question

Use the three steps to solve the problem.

Answer 1

Try this option (see the attacthed file; answer is marked with red colour); note, that

$t_{c-} = upstream \ time; \ t_{c+}=downstream \ time.$

answer: 2 m/h.

Answer 2

Answer:

Let x be the speed of current ( miles per hour ),

Thus, as per statement,

The speed of boat in still water = 5x miles per hour,

⇒ The speed in upstream = 5x - x = 4x miles per hour,

And, the speed in downstream = 5x + x = 6x miles per hour,

We know that,

$Time = \frac{Distance}{Time}$

Given distance = 12 miles,

So, the time taken in upstream = $\frac{12}{4x}=\frac{3}{x}\text{ hour}$

And, the time taken in downstream = $\frac{12}{6x}=\frac{2}{x}\text{ hours}$

Total time taken = 2½ hours

$\implies \frac{3}{x}+\frac{2}{x}=2\frac{1}{2}$

$\implies \frac{5}{x}=\frac{5}{2}$

$\implies x = 2$

Hence, the speed of current is 2 miles per hour.