Question 1178123: There are 10 identified points on a number line. How many possible rays can
be drawn using the given points?
Found 2 solutions by amarjeeth123, ikleyn:
Answer by amarjeeth123(569)   (Show Source):
You can put this solution on YOUR website! We need two points to form a ray.
This is a combination question.
Number of possible rays=C(10,2)=(10!)/(8!)(2!)=45
Answer=45 rays.
Answer by ikleyn(52777)  (Show Source):
You can put this solution on YOUR website! .
Tutor @amarjeeth is not right, and his answer is not correct.
If to accept the conception, that a ray is determined by a pair of points,
then these pairs must be considered as ORDERED (an order does matter),
and the number of different pairs and different rays will be 10*9 = 90 (not 45 (!) ).
In this problem, we work with PERMUTATIONS of 10 points, taken 2 at a time, and NOT with the COMBINATIONS (!).
Again, the order of points in pairs DOES MATTER in this problem (!).
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Solved (correctly).
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