Question 1163167
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The cycle to transfer one adult across the river is this:


<pre>
    a)  Two boys, A and B, cross first in the boat.


    b)  Then boy B returns back alone, leaving boy A on the other bank of the river.


    c)  Then 1-st adult cross the river alone in the boat.


    d)  Then boy A returns back alone.
</pre>

After these crossings, one adult is transferred to the opposite bank.



Repeat this cycle as many times until all 4 adults are transferred to the opposite bank of the river.


After that, transferring boys is a simple problem, which you can analyse by similar manner on your own, without my help.