• We are pleased to announce that the winner of our Feedback Prize Draw for the Winter 2024-25 session and winning £150 of gift vouchers is Zhao Liang Tay. Congratulations to Zhao Liang. If you fancy winning £150 worth of gift vouchers (from a major UK store) for the Summer 2025 exam sitting for just a few minutes of your time throughout the session, please see our website at https://www.acted.co.uk/further-info.html?pat=feedback#feedback-prize for more information on how you can make sure your name is included in the draw at the end of the session.
  • Please be advised that the SP1, SP5 and SP7 X1 deadline is the 14th July and not the 17th June as first stated. Please accept out apologies for any confusion caused.

Assignment X4, Q4.5

A

ALEX_AK

Member
Hello,

Is it correct if I just find

P(X>=25)=(50C25)*0.4^24*0.6*25
= 0.0405

This is also the size of the test. Am I right? Isn't it faster doing it this way? Why must we use the Normal Approx as in the solution?
 
From your formula it looks like you're calculating P(X=25), but the question is asking for P(X>=25)
P(X>=25) = P(X=25) + P(X=26) + ... + P(X=50)

You could calculate this using the probability function, but you'd need to calculate and sum all the individual probabilities, so it's quicker to use the normal approximation.
 
Back
Top