SOLUTION: a school with 60 teachers is on alert during a nighttime storm to inform teachers whether the school will open the next day , the princeipal will call four teachers each of whom

Question 1188811: a school with 60 teachers is on alert during a nighttime
storm
to inform teachers whether the school will open the next day , the princeipal will call four teachers
each of whom will then call 2 others
and each of these will again call 2 others
so on untill all 60 have been contacted
how many people have to make 2 calls?
Answer by ikleyn(52876) (Show Source): You can put this solution on YOUR website!
.

To solve the problem, I prepared this Table below


       T            A            B            L            E


    step                             how many           how mamy 
     #                             teachers know    teachers don't know

     1        a principal               4              60 - 4 = 56
            calls to 4 teachers

     2        4 teachers call
            to 8 other teachers      4 +  8 = 12       56 - 8 = 48 

     3        8 teachers calls
            to 16 other teachers    12 + 16 = 28       48 - 16 = 32 

     4       16 teacher calls
            to 32 other teachers    28 + 32 = 60       32 - 32 =  0 



Now from the table, the number of people (= of teachers) who made 2 calls is  4 + 8 + 16 = 28.


ANSWER.  The number of people who made 2 calls is  28.

Solved.

/////////////

Now, as you see this solution and this table, you can, probably, organize
your arguments in other, more compact form to produce your own solution.

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