How many permutations of 5 objects taken 3 at a time are there?
Answer and explanation
Correct answer: D.
- Step 1: P(n, r) = n!/(n − r)!. Step 2. P(5, 3) = 60. **Answer: . Why not the others:** is what you get if you count combinations. is what you get if you multiply n by k. is what you get if you allow repetition.
Practise more Matrices, calculus and coordinate geometry.
Free questions with an explanation for every one, and full timed WBJEE mock tests.
More Matrices, calculus and coordinate geometry questions
- Find the determinant of the 3×3 matrix with rows (-2, 0, 3); (-1, 5, -1); (2, 1, -1).
- If A has rows (3, -3) and (3, -1) and B has rows (-3, 4) and (3, 2), find the entry in row 2, column 1 of AB.
- Find the coordinates of the focus of the parabola y² = 12x.
- Find a × b for a = 3i + 4j − 1k and b = 2i − 2j + 3k.
- Solve dy/dx = 2x with y(0) = -1. What is y(3)?
- How many permutations of 10 objects taken 3 at a time are there?