The correct option is D If r≠s, then the possible number of solutions is 8
Given : 10Cr+2⋅ 10Cr−1+ 10Cr−2= 12Cs
For combination to be defined
10≥r≥2
Now,
10Cr+ 10Cr−1+ 10Cr−1+ 10Cr−2= 11Cr+ 11Cr−1= 12Cr
Therefore,
12Cr= 12Cs
When r=s, then
r=2,3,4,5,6,7,8,9,10
The number of solutions is 9
When r+s=12, then
(r,s)=(2,10),(3,9),(4,8),(5,7),(7,5),(8,4),(9,3),(10,2)
The number of solutions is 8