- CFA Exams
- CFA Level I Exam
- Study Session 2. Quantitative Methods (1)
- Reading 8. Probability Concepts
- Subject 10. Principles of Counting
CFA Practice Question
How many three-digit numbers can you form using the digits 1, 3, 5, 7, and 9 without a repeating a digit within the number to be formed?
A. 20
B. 60
C. 125
User Contributed Comments 9
| User | Comment |
|---|---|
| haarlemmer | The solution choose 3 out of 5 5C3 this three number can be arranged in order 3! the answer 5C3*3! |
| johnsk | It's a permutation: 135 != 315 so the order does matter. 3P5 = 5!/(5-3)! = 60. |
| Eckhardt1978 | 5!/(5-3)! |
| armanaziz | Note: nPr = n!/(n-r)! nCr = n!/(n-r)!r! |
| dealsoutlook | its 5P3 and not 3P5 |
| sheenalim | ok, what if the number to be formed can have only 2 repeated digits? i think the answer would be: 5 x 4 x 4 = 80 correct me if i'm wrong. |
| clarelau | Sheennalim: Repeated digits are not allowed. SO either 335 or 333 is incorrect. It's 5P3=60 |
| peteypete | you dont need the nPr just 5x4x3 |
| Rsanches | 5!/(5-3)!=60 |