1. 5C3+5C3/10C3
2. 20/12P3 [A-J=10 possibility and reversely another 10 possibilities]
3. 10P2*8P2*6P2* 4P2 * 2P2= 10!
4. XCn X+1Cn+1
n+1 X+1
obviously X+1>n+1, So, Ans is B
5.12Cx+p=12Cx
or, 12=x+p+x=2x+p
putting the value of P in the 1st relation, All the value satisfy the relation except, © P=3