450 ohms is 30 above the mean, which is 30/12=2.5 standard deviations. 99.38% of resistors are below 450 ohms. 450.5 ohms is 30.5 above the mean, 30.5/12=2.542 SDs. 99.45% of resistors are below 450.5 ohms. Therefore, the percentage of resistors between 450 and 450.5 is 99.45-99.38=0.07%. This is an estimate of resistors at around 450 ohms or approximately equal to 450 ohms. The percentage of resistors of 450 ohms or above is 100-99.38=0.62%.