Question 927115
mean = 300
P(x &#8804; 290) = P( z < -10/(50/sqrt(15)) =P(z < -.7746) 
Using a TI calculator 0r similarly a Casio fx-115 ES plus
P(x &#8804; 290) =P(z < -.7746) = normalcdf(-100, -.7746)= .2193  0r 21.93%