Sara has just joined Facebook. She has 5
friends. Each of her five friends has twenty five friends. It is found that at least
two of Sara’s friends are connected with each other. On her birthday, Sara
decides to invite her friends and the friends of her friends. How many people
did she invite for her birthday party?

(A) ≥
105 (B) ≤ 123 (C) < 125 (D)
≥ 100 and ≤ 125 (E) ≥ 105 and ≤ 123

*Solution:**:*

*The key point*
“Each of Sara’s 5 friends has twenty five friends” =>

*Sara is one among these 25 friends*.
I call this as ‘Facebook Logic’. If A is in friend-contacts
of B, then B is also in the friend-contacts of A.

So, in normal case, Sara has to invite 24 contacts of each
of her 5 friends along with those 5 friends (ie., 5 + 5*24 = 125). But this is
not end of story. It is also given that,

“

*At least two of Sara’s friends are connected with each other*”:
Here ‘at least two’ is another point to note. If two
of 5 friends of Sara are connected with each other, then each one of this pair has
23 contacts (excepting Sara and the other friend in the pair). Each of the remaining
3 of Sara’s friends has got 24 contacts (excepting Sara). So if Sara invites
all, there are 5 + 2*23 + 3*24 =

**invitees in all.***123*
“

*At least two*” hints us that -at maximum, all the 5 friends of Sara has the other four friends in their contacts. Then each of these 5 friends has 20 contacts (excepting Sara and the other 4). So if Sara invites all, there are 5 + 5*20 =**invitees in all.***105*
Finally we arrived at the answer: The count of invitees
ranges from

*.*__105 to 123__
grt job

ReplyDeleteaccording to testfunda and time edu. answer to this problem is <=123 .i.e. minimum 25 max 123.so which is correct.what is flaw in that method .

ReplyDelete