Geometric distribution:A teacher provides pizza for his clas

[wind]

A teacher provides pizza for his class if they earn an A-average on any test. The probability of the class getting an A-average on one of his tests is 8%. What is the probability that the class will not earn a pizza for the first 7 tests?

\(\displaystyle \L\ P(x)=q^{x}p\)

so if x is the number of failures and falures would be getting an an A average, then x=7 right? so

\(\displaystyle \L\ P(x)=\frac{92}{100}^{7}\frac{8}{100}\)

\(\displaystyle \L\
P(x)=0.0446277281\)

...but that answer is wrong

can someone tell me what I did wrong?


Thanks

 

[JakeD]

Re: Geometric distribution:A teacher provides pizza for his

A teacher provides pizza for his class if they earn an A-average on any test. The probability of the class getting an A-average on one of his tests is 8%. What is the probability that the class will not earn a pizza for the first 7 tests?

\(\displaystyle \L\ P(x)=q^{x}p\)

so if x is the number of failures and falures would be getting an an A average, then x=7 right? so

\(\displaystyle \L\ P(x)=\frac{92}{100}^{7}\frac{8}{100}\)

\(\displaystyle \L\
P(x)=0.0446277281\)

...but that answer is wrong

can someone tell me what I did wrong?


Thanks

You've given the probability the first A-average occurs on the 8th test. (That's what the geometric distribution is for.) But the question only says the first 7 tests will not have an A-average. It says nothing about the 8th test. So leave the 8th test out of your probability.

 

[wind]

Thanks JakeD!

It says nothing about the 8th test. So leave the 8th test out of your probability.

so would it be

\(\displaystyle \L\ P(x)=\frac{92}{100}^{7}\frac{8}{100}^{0}\)