Given:
1≤x,y≤25
And, x,y are distinct integers.
Let
x+y=5k, where k∈N
So, we have
| x | y | Number of ways | |
| 5λ i.e, 5,10,15,20,25 | 5λ i.e, 5,10,15,20,25 | Since, x and y are distinct integers, so we cannot pair (5,5),(10,10),...(25,25) | 20 |
| 5λ+1 i.e., 1,6,11,16,21 | 5λ+4 i.e., 4,9,14,19,14 | 25 | |
| 5λ+2 i.e, 2,7,12,17,22 | 5λ+3 i.e., 3,8,13,18,23 | 25 | |
| 5λ+3 i.e., 3,8,13,18,23 | 5λ+2 i.e, 2,7,12,17,22 | 25 | |
| 5λ+4 i.e., 4,9,14,19,14 | 5λ+1 i.e, 1,6,11,16,21 | 25 |