Answer : Given: 20Cr = 20Cr–10 Need to find: Value of 17Cr We know, one of the property of combination is: If nCr = nCt, then, (i) r = t OR (ii) r + t = n We can’t apply the property
- So we are going to use property (ii) 20Cr = 20Cr–10 By the property (ii), ⇒ r + r – 10 = 20 ⇒ 2r = 30 ⇒ r = 15 Therefore, 17C15 = 136.