Probability Question 4
Question 4 - 25 January - Shift 1
Let $x$ and $y$ be distinct integers where $1 \leq x \leq 25$ and $1 \leq y \leq 25$. Then, the number of ways of choosing $x$ and $y$, such that $x+y$ is divisible by 5 , is
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Answer: (120)
Solution:
Formula: Probability of occurrence of an event
$ x+y=5 \lambda $
Cases :
| X | y | Number of ways |
|---|---|---|
| 5λ | 5λ | 20 |
| 5λ + 1 | 5λ + 4 | 25 |
| 5λ + 2 | 5λ + 3 | 25 |
| 5λ + 3 | 5λ + 2 | 25 |
| 5λ + 4 | 5λ + 1 | 25 |
| Total | 120 |
