Year 12s: what will be the first way you research your future options? >>

Binomial distribution help!

I struggle how to find a value once it can't be gained from using the table. hard to explain so ill have to use a question.

The probability of producing a read flower is 0.6. A gardener plants 20 of these bulbs.

Find the probability that the number of read flowers produces is at least 12.

I know you have B(20, 0.6) then B(20,0.4)

at least 12 = (x greater than equal to 12) but looking at the answer/ mark scheme they've used (x less than or equal to 8). How do you get this?

Reply 1

MikeySwansea

Hi mate, hard to explain this one on here but I'll give it a shot.

You've sussed the hardest part of it:

If X - B(20,0.6) then 'X - B(20,0.4)

So we are looking for the Probability that X>=12. Just think about it. If X is going to be 12,13,14.....20. Then 'X has to be 8,7,6........0

So the probability of X>=12 is equal to the probability of 'X<=8.

Now we can use the table.