QR- rate problem

[Ocean5]

---

Members do not see this ad.

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?

 

[dmddream]

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?

 

[Ocean5]

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.

 

[dmddream]

is 5.56 one of the answers

 

[Ocean5]

is 5.56 one of the answers

Ohh about the answers. These are only choices:

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

 

[Streetwolf]

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.

 

[Ocean5]

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.

👍 Thank You.

 

[REH]

Ocean5,

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

REH.

 

[Ocean5]

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.