Permutations And Combinations Question 177

Question: The number of triangles that can be formed with 10 points as vertices, n of them being collinear, is 110. Then n is

Options:

A) 3

B) 4

C) 5

D) 6

Show Answer

Answer:

Correct Answer: C

Solution:

  • [c] Out of 10 points let n points be collinear. Then the number of triangles is $ ^{10}C_3{{-}^{n}}C_3=110 $ or $ \frac{10\times 9\times 8}{6}-\frac{n(n-1)(n-2)}{6}=110 $ or $ n(n-1)(n-2)=60 $ or $ n=5 $