Maths-
General
Easy

Question

The value of  if blank space presuperscript n C subscript 3 colon blank to the power of n minus 1 end exponent C subscript 4 equals 8 colon 5 is

  1. 9    
  2. 7    
  3. 8    
  4. 10    

hintHint:

This question is in reference to the chapter Permutations and Combinations. Apply the formula of combination and find the value of n with the help of the ratio.

The correct answer is: 8


    scriptbase C subscript 3 space colon space scriptbase C subscript 4 space equals space 8 colon 5 end scriptbase presuperscript n minus 1 end presuperscript end scriptbase presuperscript n

S o comma
fraction numerator scriptbase C subscript 3 end scriptbase presuperscript n over denominator scriptbase C subscript 4 end scriptbase presuperscript n minus 1 end presuperscript end fraction space equals space 8 over 5
fraction numerator begin display style fraction numerator n factorial over denominator open parentheses n minus 3 close parentheses factorial 3 factorial end fraction end style over denominator begin display style fraction numerator open parentheses n minus 1 close parentheses factorial over denominator open parentheses n minus 1 minus 4 close parentheses factorial 4 factorial end fraction end style end fraction space equals space 8 over 5
fraction numerator begin display style fraction numerator n over denominator open parentheses n minus 3 close parentheses open parentheses n minus 2 close parentheses open parentheses n minus 1 close parentheses open parentheses n close parentheses open parentheses 3 close parentheses open parentheses 2 close parentheses open parentheses 1 close parentheses end fraction end style over denominator begin display style fraction numerator open parentheses n minus 1 close parentheses n over denominator open parentheses n minus 5 close parentheses open parentheses n minus 4 close parentheses open parentheses n minus 3 close parentheses open parentheses n minus 2 close parentheses open parentheses n minus 1 close parentheses open parentheses n close parentheses open parentheses 4 close parentheses open parentheses 3 close parentheses open parentheses 2 close parentheses open parentheses 1 close parentheses end fraction end style end fraction space equals space 8 over 5
fraction numerator begin display style 1 over 1 end style over denominator begin display style fraction numerator open parentheses n minus 1 close parentheses over denominator open parentheses n minus 5 close parentheses open parentheses n minus 4 close parentheses 4 end fraction end style end fraction space equals space 8 over 5
fraction numerator open parentheses n minus 5 close parentheses open parentheses n minus 4 close parentheses 4 over denominator open parentheses n minus 1 close parentheses end fraction space equals space 8 over 5
fraction numerator open parentheses n minus 5 close parentheses open parentheses n minus 4 close parentheses over denominator open parentheses n minus 1 close parentheses end fraction space equals space 2 over 5
5 open parentheses n minus 5 close parentheses open parentheses n minus 4 close parentheses space equals space 2 open parentheses n minus 1 close parentheses
5 open parentheses n squared space minus 9 n space plus space 20 close parentheses space equals space 2 n space minus space 2
5 n squared space minus space 45 n space plus space 100 space equals space 2 n space minus space 2
5 n squared space minus space 45 n space minus space 2 n space plus space 100 space plus space 2 space equals space 0
5 n squared space minus space 47 n space plus space 102 space equals space 0

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