Chapter 6 - Percent - Review Exercises - Page 464: 30

$\frac{unknown}{1280} = \frac{88}{100}$ Part = unknown Whole= 1280 Percent = 88

$\frac{Part}{Whole} = \frac{Percent}{100}$ Now 88 % of the door keys cut will operate properly. And there are 1280 keys cut. i.e. $\frac{unknown}{1280} = \frac{88}{100}$