What is the number of student that get less than $144$ marks if the number of students taken the test is $2500$?
mean $=160, SD = 8$, mound-shaped distribution
I solved it like this:
First:
$z$-score $(144)= (144 - 160)/8 = -2$ $SD = -2 \to 95$% $(100 - 95) / 2 = 2.5$%
Second: Is it $2.5$%$ \cdot 2500 = 625$ or $6250$?
Thanks