If  15Cr+1:15C3r=3:11 then value of r is

Note that 0≤3r≤15⇒0≤r≤5. Also, 15!(14−r)!(r+1)!×(3r)!(15−3r)!15!=311⇒ (3r)!(15−3r)!(14−r)!(r+1)!=311                       1For the denominator, to be divisible by 11,11∣(14−r)!Setting  14−r=11. ⇒ r=3Putting r = 3, in LHS of (1) we getLHS of  (1) 9!6!11!4!=6×511×10=311= = RHS of (1) ∴ r=3