Mary Jane is stranded on a deserted island in the middle of a huge and deep lake. She cannot swim and all she has is two strings, each one one foot long. All of the boats she would be able to use are docked at the shore 4 miles away from her. 2 hours later, she is on the shore of the lake. How did she get across the lake?

  • 1
    $\begingroup$ May you please tell us if you are meant to use the strings at all? Because there are many answers so far, and none of them use the strings. $\endgroup$ – PotatoLatte Jul 22 '18 at 13:07
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    $\begingroup$ Downvoted because according to AstralBee's Answer this is a verbatim copy of a puzzle on another website, which doesn't really have a great solution. $\endgroup$ – Snow Jul 23 '18 at 13:54

Using the strings,

Mary ties them in a knot and smashes the resulting union on some island rocks for one hour and 59 minutes. She then looks at the result and asks, "Am I still on the Island, string?"
The string replies, "I'm a frayed knot."

  • $\begingroup$ If this was the answer, I'd lose my mind lol +1 $\endgroup$ – elarr Jul 24 '18 at 15:24

This riddle has been copied from this page, where the answer is given as:

The lake was frozen so she was able to walk across, making it to the shore.

It probably is an example of a classic lateral thinking puzzle but to be honest I think it is very poor. There is no logic involved and ANY contrived "deus ex machina" answer could be substituted.

Nothing in the question either alludes to or excludes the possibility of the lake being frozen, but by the same token nothing excludes the possibility of Mary-Jane being rescued by a helicopter either. Further, Mary Jane is described as being "stranded" on the island, but a lake does not freeze in 2 hours so it must have been frozen right from the start in which case she was never really "stranded". Terrible puzzle.


How did she get across the lake?

What If lake was FROZEN

and finally

she was able to walk across, making it to the shore.

  • $\begingroup$ This seems to be a surprisingly sensible answer, because otherwise it would be very weird that all the boats are docked. The strings still go unexplained, though. $\endgroup$ – Bass Jul 22 '18 at 9:40

I would guess:

that these boats are docked four miles away on the island.

which further suggests:

Mary Jane could walk over to the boats in enough time. According to Google, it takes the average person about 20 minutes to walk a mile. Thus, if she walked the entire time, she could potentially make it to the boats in an hour and 20 minutes. This leaves forty minutes if the boats are ready to go immediately.

This makes a few assumptions:

First, Mary Jane needs to know how to operate the boat. Second, they should be speedy boats to get offshore within the allotted time. Third, Mary Jane is able to traverse the terrain.


The most obvious answer, which I confess I hope is wrong, is that

she didn't get across the lake


after two hours she is on the shore of the lake on the island.

If this is right, then

the last sentence, for my taste, crosses the line between clever misdirection and outright deception, and I must direct the questioner's attention to this famous comic strip: https://xkcd.com/169/.


I would like to suggest an alternative answer

Mary Jane is a bird

And so

She just flies over the lake.


I remember hearing this puzzle a long time ago. I tried looking up the source, but I couldn't find it.

Anyways, the answer has been said by others, but they left out one crucial part: the strings we're not used in their answers.

The lake was frozen, and she had two shoelaces on her ice skates.


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