## pakinam 2 years ago I throw darts repeatedly. Assume that on each single throw, my chance of hitting the bullseye is 10%, independently of all other throws. I decide to throw until I have hit the bullseye 3 times. What is the chance that I throw exactly 30 times?

1. reemii

you have this info: 30 throws, last throw is a BE (bullseye). P(BE)=0.1. But you don't know where the other two BE's are. So it's like that: (29 hits with 2BE's) and 1BE. Does this help?

2. pakinam

ahh ok

3. reemii

you have to use a combintation "C(n,k)" factor in the computation of the probability of (29 throws with 2 BE's), then multiply by P(1BE).

4. sarah10

is the ans 40.6

5. reemii

No, the answer must be a number of [0,1]. but it should be $$P(\text{2 BE's in 29 throws})\times P(\text{1 BE}) = \binom{29}{2}0.1^{2}\,0.9^{27} \times 0.1$$. I got 0.02360879322323428... as anwer.

6. sarah10

is it the right ans ..... actually in frst attempt i got the the wrong ans

7. reemii

it's right.

8. sarah10

thank you soooo much 4 helping me

9. reemii

yw

10. pakinam

0.0236 is wrong

11. reemii

12. pakinam

i got wrong when i entered this answer

13. Khlara

@pakinam i gt it correct