If one test (on screening paper basis) was conducted on Batch A, maximum number of marks is ( 90 × 3 ) = 270.4 students get the marks lower than 80 . Coaching institute decide to inform their guardian

Question

If one test (on screening paper basis) was conducted on Batch A, maximum number of marks is $(90 \times 3) = 270.4$ students get the marks lower than 80 . Coaching institute decide to inform their guardians, that is why their result card were sent to their home. The number of ways, in which all the letters were put in wrong envelopes, is

TestHub · Accepted Answer

The number of ways in which all the letters are in wrong envelopes

$= 4! (1 - \frac{1}{1 !} + \frac{1}{2 !} - \frac{1}{3 !} + \frac{1}{4 !})$

$= 4! (\frac{1}{2} - \frac{1}{6} + \frac{1}{24}) = 12 - 4 + 1 = 9$

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