Q44 / 98 · NTA Abhyas (JEE Main) 2020 · Mathematics · Permutation Combination

The position vector of the point P is π→=xi^+yj^ +zk^, where x,y,z∈N. If a→=i^+j^+k^ and π→.a→=10, then the number of possible positions of point P is equal to

  • Correct answer
    A
    36
  • B
    72
  • C
    66
  • D
    54

Solution

π→.a→=10
⇒x+y+z=10
The required number of positions
= The number of positive integral solutions of x+y+z=10
=C3-110-1
=9×82=36

Hence, the correct answer is option: 'A'.

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