Each plant has a probability of 3/4 of having red blosoms and the blossom colours of separate plants are independent. What is the probability of obtaining at least 80 red-blossomed plants when 120 plants are grown from seeds?
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So where are you having a problem?
Right, well as it stands it's a binomial, B~(120, 3/4)
The normal approximates the binomial if np>5 and nq>5 (where q=1-p)
That's satisfied here.
The approximation is X~N(np, npq)
So X~N(90, 22.5) and we need P(X>(or equal to)80)
As it's "greater than or equal to" we subtract 0.5 (continuity correction)
So we need P(X>79.5)
Can you do it now?
Right, well as it stands it's a binomial, B~(120, 3/4)
The normal approximates the binomial if np>5 and nq>5 (where q=1-p)
That's satisfied here.
The approximation is X~N(np, npq)
So X~N(90, 22.5) and we need P(X>(or equal to)80)
As it's "greater than or equal to" we subtract 0.5 (continuity correction)
So we need P(X>79.5)
Can you do it now?