Originally Posted by

**mathaddict** i am not sure where my mistake is . Can someone pls check for me .

Q : In a test , the math marks if candidates at a certain centre are normally distributed with a mean of 55 marks and a standard deviation of 5 marks . If a sample of 5 students is chosen at random , find the probability that at least one student obtains marks of less than 60 .

My working :

Let X be the random variable of the math marks of the candidates ..

X - N ( 55 , 25 )

P ( X < 60 ) = 0.84134

then , let Y be the random variable of the number of students obtaining marks less than 60 .

X - B ( 5 , 0.84134 )

therefore P ( Y ≥ 1 ) = 0.999 ----- my answer

But the answer given is 0.5784

Where did i go wrong ??