Question 970038
The lowest 10% on the normal distribution is at z=-1.28

-1.28=  (score-mean)/sd

-1.28= (score-80)/10
multiply by 10 both sides

-12.8=score -80

add 80 to both sides

score=67.2
if no decimals, 68 would not quite include the lowest 10%, and 67 would include a little more than 10%.