Chapter 6 - Normal Probability Distributions - 6-3 Applications of Normal Distributions - Basic Skills and Concepts - Page 268: 15

0.4972

$z_1=\frac{value-mean}{standard \ deviation}=\frac{110-100}{15}=0.667.$ $z_2=\frac{value-mean}{standard \ deviation}=\frac{90-100}{15}=-0.667.$ Using the table, the value belonging to 0.667: 0.7486, the value belonging to -0.667: 0.2514. 0.7486-0.2514=0.4972.