QR ques from destroyer

[Dental2000]

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its question 64 in the 2010 DAT destroyer for those of you who like the question on paper...

Q) The weatherman tells you that there is a 70% chance of rain each day for the next 3 days. What is the probability it will rain 2 out the 3days?

1) 2/3
2)7/10
3) 49/1000
4)441/1000
5) 189/1000

the explanation in the book used some probability formula. Is there another way to get to the answer without having to use a long ass formula?

 

[JamesBourne]

its question 64 in the 2010 DAT destroyer for those of you who like the question on paper...

Q) The weatherman tells you that there is a 70% chance of rain each day for the next 3 days. What is the probability it will rain 2 out the 3days?

1) 2/3
2)7/10
3) 49/100
4)441/1000
5) 189/1000

the explanation in the book used some probability formula. Is there another way to get to the answer without having to use a long ass formula?

Can't think of any other ways besides using the binomial equation for this problem. That probably is the easiest and fastest way to handle these type of problems. Btw, isn't choice 3 supposed to be 49/1000 instead of 49/100?

 

[Dental2000]

yeah its 49/1000, forgot the extra 0....but thats not the answer so it shoudnt throw ppl off

 

[JamesBourne]

yeah its 49/1000, forgot the extra 0....but thats not the answer so it shoudnt throw ppl off

🙂 just checking, anyways like I said it wouldn't hurt to memorize the binomial equation since these questions come up pretty routinely on practice questions.
n = 3 days k = 2 days chance of raining = 7/10 (70/100) not raining 3/10(1-7/10), (3*2*1/2*1)*(7/10)^2*(3/10)^1 = 441/1000, quick tip here is that you always power the event that will happen first and then figure out the other prob. and power next