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Permutations and Combinations question

2021 · 20 Jul · Shift 1 · Q43
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Permutations and Combinations question

2021 · 20 Jul · Shift 1 · Q43

JEE MainMathematicsPermutations and CombinationsNumerical+4 / −1
There are 15 players in a cricket team, out of which 6 are bowlers, 7 are batsman and 2 are wicketkeepers. The number of ways, a team of 11 players be selected from them so as to include at least 4 bowlers, 5 batsman and 1 wicketkeeper, is ‾\underline{\hspace{2cm}}​.
Numerical answer
View written solutionFree

Correct answer: 777

  1. Classify the players

There are:

  • 666 bowlers
  • 777 batsmen
  • 222 wicketkeepers

We need to form a team of 111111 such that it contains:

  • at least 444 bowlers
  • at least 555 batsmen
  • at least 111 wicketkeeper

Let the selected numbers be:

  • bowlers =b= b=b
  • batsmen =m= m=m
  • wicketkeepers =w= w=w

Then b+m+w=11b+m+w=11b+m+w=11 with constraints b≥4,m≥5,w≥1b\ge 4,\quad m\ge 5,\quad w\ge 1b≥4,m≥5,w≥1 Also, b≤6,m≤7,w≤2b\le 6,\quad m\le 7,\quad w\le 2b≤6,m≤7,w≤2


  1. Find all possible compositions (b,m,w)(b,m,w)(b,m,w)

Since minimum required players are: 4+5+1=104+5+1=104+5+1=10 we need 111 extra player beyond the minimum.

So distribute this 111 extra among bowlers, batsmen, wicketkeepers, respecting upper limits.

Possible cases:

  • (4,5,2)(4,5,2)(4,5,2)
  • (4,6,1)(4,6,1)(4,6,1)
  • (5,5,1)(5,5,1)(5,5,1)

These are the only valid possibilities.


  1. Count selections for each case

Case 1: (b,m,w)=(4,5,2)(b,m,w)=(4,5,2)(b,m,w)=(4,5,2)

Choose:

  • 444 bowlers from 666: (64)\binom{6}{4}(46​)
  • 555 batsmen from 777: (75)\binom{7}{5}(57​)
  • 222 wicketkeepers from 222: (22)\binom{2}{2}(22​)

Number of ways: (64)(75)(22)=15⋅21⋅1=315\binom{6}{4}\binom{7}{5}\binom{2}{2}=15\cdot 21\cdot 1=315(46​)(57​)(22​)=15⋅21⋅1=315

Case 2: (b,m,w)=(4,6,1)(b,m,w)=(4,6,1)(b,m,w)=(4,6,1)

Choose:

  • 444 bowlers from 666: (64)\binom{6}{4}(46​)
  • 666 batsmen from 777: (76)\binom{7}{6}(67​)
  • 111 wicketkeeper from 222: (21)\binom{2}{1}(12​)

Number of ways: (64)(76)(21)=15⋅7⋅2=210\binom{6}{4}\binom{7}{6}\binom{2}{1}=15\cdot 7\cdot 2=210(46​)(67​)(12​)=15⋅7⋅2=210

Case 3: (b,m,w)=(5,5,1)(b,m,w)=(5,5,1)(b,m,w)=(5,5,1)

Choose:

  • 555 bowlers from 666: (65)\binom{6}{5}(56​)
  • 555 batsmen from 777: (75)\binom{7}{5}(57​)
  • 111 wicketkeeper from 222: (21)\binom{2}{1}(12​)

Number of ways: (65)(75)(21)=6⋅21⋅2=252\binom{6}{5}\binom{7}{5}\binom{2}{1}=6\cdot 21\cdot 2=252(56​)(57​)(12​)=6⋅21⋅2=252


  1. Add all cases

Total number of valid teams: 315+210+252=777315+210+252=777315+210+252=777


  1. Final Answer

The number of ways is 777\boxed{777}777​


  1. Comparison with stored correct answer

Stored correct answer = 777777777

Our derived answer also equals 777777777, so they agree.

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