6 thoughts on “PnC : Summing Up

  1. Sorry to post this question in random thread…But since its quite relevant I m posting It..

    Answer the questions independently of each other.

    There are 12 points in a plane, out of which only four are collinear and the remaining eight are non-collinear. How many non-overlapping straight line segment can be drawn by joining any two of these points?
    Actually I got two different solution within IMS Test papers..

  2. Sir,
    In the formula for type where we distribute ‘x’ distinct objects into ‘y’ distinct groups AND there is arrangement within groups, shouldn’t it read ” Send n distinct objects to r distinct groups”,
    since the answer is P(n+r-1, n) ?

  3. Sir, in the 6th case of arranging r out of n in circle…can we do it by first selecting r out of n, then arranging them in (r-1)! ways…so nCr*(r-1)!……?

    • I don’t think that would work; the n are not distinct to begin with. In the situation, I meant n positions and r (<=n) people to be arranged in them, I think what you are saying would work fine for n people and r positions. Sorry for the ambiguity!


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s