Here's the problem:
On a quiz of 10 questions, a student guesses on all of them. Each question has 4 possible answers, with only 1 being correct, and each is independent of every other question.
What is the probability of guessing more than 8 correctly? P(x > 8)
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This is what I did...
number of trials (n) = 10
probability of success (p) = 0.25
number of successes (x) = 9 and 10
P(9) + P(10) = (answer)
This is the equation I used
[(10 C 9) (0.25^9)(0.75^1)] + [(10 C 10)(0.25^10)(0.75^0)]
The 10 C 9 thing is 10 combination 9, btw.
I keep getting (what I think is) some outrageous number. Even when I use the calculator I get about
2.9563...which in percent form would be about 295.64%
How can the probability of something like getting 10 out of 10 questions correct on a test be 295%??
On a quiz of 10 questions, a student guesses on all of them. Each question has 4 possible answers, with only 1 being correct, and each is independent of every other question.
What is the probability of guessing more than 8 correctly? P(x > 8)
======================================…
This is what I did...
number of trials (n) = 10
probability of success (p) = 0.25
number of successes (x) = 9 and 10
P(9) + P(10) = (answer)
This is the equation I used
[(10 C 9) (0.25^9)(0.75^1)] + [(10 C 10)(0.25^10)(0.75^0)]
The 10 C 9 thing is 10 combination 9, btw.
I keep getting (what I think is) some outrageous number. Even when I use the calculator I get about
2.9563...which in percent form would be about 295.64%
How can the probability of something like getting 10 out of 10 questions correct on a test be 295%??
-
[(10 C 9) (0.25^9)(0.75^1)] + [(10 C 10)(0.25^10)(0.75^0)]
= 2.95639e-5
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i don't see anything wrong in the formula.
must be something to do with inputting into your calculator.
try simplified version with 10*.25^9*.75 + .25^10 = 2.95639e-5
your AD
======
2.95639e-5 means 2.95639 x 10^-5 = 0.0000295639 or 0.00295639%
= 2.95639e-5
--------------------
i don't see anything wrong in the formula.
must be something to do with inputting into your calculator.
try simplified version with 10*.25^9*.75 + .25^10 = 2.95639e-5
your AD
======
2.95639e-5 means 2.95639 x 10^-5 = 0.0000295639 or 0.00295639%
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The probability of guessing all ten correctly is 0.25^10
The probability of guessing nine of the ten correctly is 10 * 0.25^9*0.75
Hence, the probability of guessing more than 8 (i.e 9 or 10) is 0.25^10 + 10 * 0.25^9*0.75
The probability of guessing nine of the ten correctly is 10 * 0.25^9*0.75
Hence, the probability of guessing more than 8 (i.e 9 or 10) is 0.25^10 + 10 * 0.25^9*0.75