maths probability question

how do I approach part C? can anyone suggest any ideas? thanks

(edited 1 year ago)

how do I approach part C? can anyone suggest any ideas? thanks

Consider: If she stops after 10, what must the last value be? And what you do know about the first 9 values?

ohh must the last value be two? so would you do 9C2 etc. to find the probability of two successes in 9 previous tries?

Original post by ghostwalker

Consider: If she stops after 10, what must the last value be? And what you do know about the first 9 values?

ohh must the last value be two? so would you do 9C2 etc. to find the probability of two successes in 9 previous tries?

Yep. So, you need exactly 2 out of the first 9 to be "2", AND the last (10th) one to be "2".

I get it now, thank you!

Original post by ghostwalker

Yep. So, you need exactly 2 out of the first 9 to be "2", AND the last (10th) one to be "2".

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