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TS EAMCET · Maths · Binomial Theorem

If Pr+122: Pr+220=11: 52 then r=

  1. A 3
  2. B 5
  3. C 7
  4. D 9
Verified Solution

Answer & Solution

Correct Answer

(C) 7

Step-by-step Solution

Detailed explanation

Pr+122: Pr+220=11: 52 Apply the formula Pnr=n!n-r! ⇒22!(22-r-1)!20!(22-r-2)!=1152 ⇒22!×(18-r)!20!×21-r!=1152 ⇒22×21×20!×(18-r)!20!×21-r×20-r×19-r×18-r!=1152 ⇒22×2121-r×20-r×19-r=1152…