Permutations And Combinations Question 108
Question: If $ ^{n}C_3+{{}^{n}}C_4>{{}^{n+1}}C_3, $ then [RPET 1999]
Options:
A) $ n>6 $
B) $ n>7 $
C) $ n<6 $
D) None of these
Correct Answer: A $ \Rightarrow n>6 $ .
Show Answer
Answer:
Solution:
Þ $ {}^{n+1}C_4>{}^{n+1}C_3(\because {}^{n}C _{r}+{}^{n}{C _{r+1}}={}^{n+1}{C _{r+1}}) $
Þ $ \frac{{}^{n+1}C_4}{{}^{n+1}C_3}>1 $
Þ $ \frac{n-2}{4}>1 $
BETA
