Answer : Given: ²⁰Cr+1 = ²⁰Cr–10 Need to find: Value of ¹⁰Cr 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 (i) here. So we are going to use property (ii) ²⁰Cr+1 = ²⁰Cr–10By the property

• , ⇒ r + 1 + r – 10 = 20 ⇒ 2r = 29 ⇒ r = 14.5. We need to find out the value of ¹⁰C But here r can’t be a rational number. Therefore the value of ¹⁰Cr can’t be find out.