How long does it take to swim?

Question

If a boy swims 5 yards in 4 seconds then in 1 second a wave pushes him back 2 yards. If this cycle continues, how long will it take him to swim out 20 yards even if only for an instant?

Answer 1

Don't be afraid to draw a picture:

 

time           distance

-----          -----------

  0                start

  4                * * * * *   (5)

  5                * * *

  9                * * * * * * * *  (8)

 10               * * * * * * 

 14               * * * * * * * * * * *    (11)

 15               * * * * * * * * *

 19               * * * * * * * * * * * * * *     (14)

 20               * * * * * * * * * * * * 

 24               * * * * * * * * * * * * * * * * *    [17)

 25               * * * * * * * * * * * * * * * 

 29               * * * * * * * * * * * * * * * * * * * *   (20)      ! DONE !

 

Since the net progress is 5-2=3 yards each 5 seconds, it will take 25 (that is 5*5) seconds to go 15 (that is, 3*5) yards after falling back.  Then going 5 yards achieves 20 yards (no falling back).

Answer 2

Hello, Kimberly,

You need some kind of picture or model.  A table is possible, such as the one below:

Q:  How long will it take to swim 20 yards?

 

 4 seconds= 5 yds.  and one second more, you subtract 2.

 

Seconds              yards

0                            0    

4                            5         0+5

1                            3          5-2

4                            8          3+5

1                            6          8-2

4                            11        6+5

_etc.________________________

total time               20           

 

I hope that this table helps you.  Just keep going until you reach 20 yards, and then, add up all the minutes to find the time that it took.  Susan C.