1. The problem is to calculate $100\% - \frac{9}{10}$.\n2. Convert $100\%$ to a decimal: $100\% = 1$.\n3. Now subtract $\frac{9}{10}$ from $1$: $$1 - \frac{9}{10} = \frac{10}{10} - \frac{9}{10} = \frac{1}{10}.$$\n4. The result is $\frac{1}{10}$ or $0.1$.