Thread: [SOLVED] simple math stats

Hi, so i have to find the probability in a random sample to find that the average lies between 475 and 540 with mean 500 and st.dev 125. the z-values i got for 475 is -1 and for 540 1.6. I look on the z-table to find that the p-value for -1 is 0.1587 and 1.6 0.05487.

The sum of those two is 0.2135 and that would be the probability right? but the answer sheet says its 0.7865. what did i do wrong? greatly appreciated if anyone can help.

nvm SOLVED it..

Originally Posted by mx70kc

Hi, so i have to find the probability in a random sample to find that the average lies between 475 and 540 with mean 500 and st.dev 125. the z-values i got for 475 is -1 and for 540 1.6. I look on the z-table to find that the p-value for -1 is 0.1587 and 1.6 0.05487.

The sum of those two is 0.2135 and that would be the probability right? but the answer sheet says its 0.7865. what did i do wrong? greatly appreciated if anyone can help.

nvm SOLVED it..

nice!