# Water current

John swims upstream. After a while, he passes the bottle, from that moment he floats for 20 minutes in the same direction. He then turns around and swims back, and from the first meeting with the bottle, he sails 2 kilometers before he reaches the bottle. What is the current speed? (John is still swimming at the same speed regardless of the current.

Result

f =  3 km/h

#### Solution:

$s_{1}=(j-f) \cdot \ 20/60 \ \\ s_{2}=2 \ \text{km} \ \\ s_{2}=f \cdot \ (\dfrac{ s_{1}+s_{2} }{ f+j } + 20/60) \ \\ 2=f \cdot \ (\dfrac{ (j-f) \cdot \ 20/60+2 }{ f+j } + 20/60) \ \\ 2=f \cdot \ (\dfrac{ (j-f)/3+2 }{ f+j } + 1/3) \ \\ \ \\ (f-3)j/ (f+j)=0 \ \\ \ \\ j,f>0 \ \\ j \ne f \ \\ \ \\ f-3=0 \ \\ f=3 \ \text{km/h}$

Our examples were largely sent or created by pupils and students themselves. Therefore, we would be pleased if you could send us any errors you found, spelling mistakes, or rephasing the example. Thank you!

Leave us a comment of this math problem and its solution (i.e. if it is still somewhat unclear...):

Be the first to comment!

Tips to related online calculators
Do you have a linear equation or system of equations and looking for its solution? Or do you have quadratic equation?
Do you want to convert velocity (speed) units?
Do you want to convert time units like minutes to seconds?

## Next similar math problems:

1. Father 7
Father is 6 times older than his son. After 4 years, the father will only be 4 times older. What are their present ages?
2. Lee is
Lee is 8 years more than twice Park's age, 4 years ago, Lee was three times as old. How old was Lee 4 years ago?
3. Three unknowns
Solve the system of linear equations with three unknowns: A + B + C = 14 B - A - C = 4 2A - B + C = 0
4. Age problems
A) Alex is 3 times as old as he was 2 years ago. How old is he now? b) Casey was twice as old as his sister 3 years ago. Now he is 5 years older than his sister. How old is Casey? c) Jessica is 4 years younger than Jennifer now. In 10 years, Jessica wi
5. Elimination method
Solve system of linear equations by elimination method: 5/2x + 3/5y= 4/15 1/2x + 2/5y= 2/15
6. Carla
Carla is 5 years old and Jim is 13 years younger than Peter. One year ago, Peter’s age was twice the sum of Carla’s and Jim’s age. Find the present age of each one of them.
7. Pooja
Pooja and Deepa age is 4:5, 4 years back it was 8:11. What is the age of Pooja now?
8. Guppies for sale
Paul had a bowl of guppies for sale. Four customers were milling around the store. 1. Rod told paul - I'll take half the guppies in the bowl, plus had a guppy. 2. Heather said - I'll take half of what you have, plus half a guppy. The third customer, Na
9. Linsys2
Solve two equations with two unknowns: 400x+120y=147.2 350x+200y=144
10. Three workshops
There are 2743 people working in three workshops. In the second workshop works 140 people more than in the first and in third works 4.2 times more than the second one. How many people work in each workshop?
11. Men, women and children
On the trip went men, women and children in the ratio 2:3:5 by bus. Children pay 60 crowns and adults 150. How many women were on the bus when a bus was paid 4,200 crowns?
12. Ball game
Richard, Denis and Denise together scored 932 goals. Denis scored 4 goals over Denise but Denis scored 24 goals less than Richard. Determine the number of goals for each player.
13. Stones 3
Simiyu and Nasike each collected a number of stones in an arithmetic lesson. If Simiyu gave Nasike 5 stones, Nasike would have twice as many stones as Simiyu. If initially, Simiyu had five stones less than Nasike how many stones did each have?
14. Children
The group has 42 children. There are 4 more boys than girls. How many boys and girls are in the group?
15. Family
Family has 4 children. Ondra is 3 years older than Matthew and Karlos 5 years older than the youngest Jane. We know that they are together 30 years and 3 years ago they were together 19 years. Determine how old the children are.
16. Theorem prove
We want to prove the sentence: If the natural number n is divisible by six, then n is divisible by three. From what assumption we started?
17. Legs
Cancer has 5 pairs of legs. The insect has 6 legs. 60 animals have a total of 500 legs. How much more are cancers than insects?