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If the papers of 4 students can be checked by any one of the 7 teachers, then the probability that all the 4 papers are checked by exactly 2 teachers, is equal to |
$\frac{12}{49}$ $\frac{6}{49}$ $\frac{9}{49}$ $\frac{15}{49}$ |
$\frac{6}{49}$ |
Total ways in which papers can be checked is equal to 74. Now two teachers who have to check all the papers can be selected in 7C2 ways and papers can be checked by them in (24 − 2) favourable ways. Thus, required probability $=\frac{{ }^7 C_2 . \left(2^4-2\right)}{7^4}=\frac{6}{49}$ |
