A ski-boat can travel 20 mph in calm water. On a river it can travel 45 miles with the current in the same time it can travel 27 miles against the currect. What is the current's rate in m/h?

A ski-boat can travel 20 mph in calm water. On a river it can travel 45 miles with the current in the same time it can travel 27 miles against the currect. What is the current's rate in m/h?
are 45 and 27 in miles or miles per hour?

are 45 and 27 in miles or miles per hour?


This is all the problem gives us. I guess the main point to consider is that both are at the same time. 45 w/t the current happens in the same time as 27 against the current.

is 5.56 one of the answers

is 5.56 one of the answers


Ohh about the answers. These are only choices:

- 4
- 5
- 13 1/3
- 18
- 80

Boat's speed is 20mph.
Current's speed is x mph.

So with the current the boat goes (20+x)mph.
Against the current the boat goes (20-x)mph.

R x T = D

Boat goes 45 miles with the current:

(20+x)*t = 45

Boat goes 27 miles against the current:

(20-x)*t = 27

So we have a system of equations:

20t + xt = 45
20t - xt = 27

Add the two:

40t + 0 = 72
t = 9/5 = 1.8

So plug that into one of the above equations:

(20+x)(9/5) = 45
20+x = 45(5/9) = 25
20+x = 25
x = 5

Current is 5 mph.

Plug in this answer to confirm.

Boat's speed is 20mph.
Current's speed is x mph.

So with the current the boat goes (20+x)mph.
Against the current the boat goes (20-x)mph.

R x T = D

Boat goes 45 miles with the current:

(20+x)*t = 45

Boat goes 27 miles against the current:

(20-x)*t = 27

So we have a system of equations:

20t + xt = 45
20t - xt = 27

Add the two:

40t + 0 = 72
t = 9/5 = 1.8

So plug that into one of the above equations:

(20+x)(9/5) = 45
20+x = 45(5/9) = 25
20+x = 25
x = 5

Current is 5 mph.

Plug in this answer to confirm.

:thumbup: Thank You.

Ocean5,

These are good problems that you're posting. Where are you finding them?

REH.

Ocean5,

These are good problems that you're posting. Where are you finding them?

REH.

Over time I have recoreded some problems that I had a harder time solving them, so I get them from my notebook. Sorry that I haven't recorded their original source. However, they are from all sources that we normally use to prepare for DAT.

I'm glad that you find them helpful.