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  • If the papers of 4 students can be checked by any one of the 7 teachers. If the probability that all the 4 papers are checked by exactly 2 teachers is <img alt="\mathrm{A}" src="https://entrancecor

If the papers of 4 students can be checked by any one of the 7 teachers. If the probability that all the 4 papers are checked by exactly 2 teachers is \mathrm{A}, then the value of \mathrm{490 \mathrm{~A}} must be

Option: 1

\frac{6}{49}


Option: 2

\frac{7}{49}


Option: 3

\frac{8}{49}


Option: 4

1


Answers (1)

best_answer

Total number of ways in which papers of 4 students, can be checked by seven teachers =7^4
Now, choosing two teachers out of 7 is \mathrm{{ }^7 C_2=21}

The number of ways in which 4 papers can be checked by exactly two teachers

\mathrm{=2^4-2=14}

\mathrm{\therefore \quad \text { Favourable ways } =(21)(14) }

\mathrm{\therefore \quad \text { Required probability } =\frac{(21)(14)}{7^4} }

\mathrm{ =\frac{6}{49} }

\mathrm{=A }

\mathrm{\therefore \quad 490 A =490 \times \frac{6}{49} }

\mathrm{=60}








 

Posted by

shivangi.shekhar

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