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📐 Mathematics  ·  Permutations and Combinations  ·  JEE

Using binomial theorem, coefficient of x³ in (1+x)<sup>7</sup> is:

Answer: 35.

  • A 21
  • B 35
  • C 15
  • D 7

Correct answer: B. 35

Explanation: 7C3 = 35. Coefficient of x<sup>r</sup> in (1+x)<sup>n</sup> is nCr.

StartABCBCACAB6 ordered outcomes (permutations); pairing AB/BA etc gives 3 combinations

Counting tree for selecting 2 items from {A, B, C} without repetition: 3 x 2 = 6 ordered arrangements.

Concept context

Counting, arrangements, and selections

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