Question

The grades on the last science exam had a mean of 89%. Assume the population of grades on science exams is known to be distributed normally, with a standard deviation of 14%. Approximately what percent of students earn a score between 75% and 89%?

Answer 1

B. 34%

Explanation:

took the test got it right

Answer 2

Are you sure the standard deviation is 14% = 0.14? I'll assume it is.


`\mathbb P(75<X<89)=\mathbb P\left((75-89)/(0.14)<(X-89)/(0.14)<(89-89)/(0.14)\right)=\mathbb P(-100<Z<0)\approx0.5`

I suspect the given standard deviation is wrong, and that you instead meant 14 (no percent). This would make the probability


`\mathbb P(75<X<89)=\mathbb P\left((75-89)/(14)<(X-89)/(14)<(89-89)/(14)\right)=\mathbb P(-1<Z<0)\approx0.3413`

which seems a more likely answer.