Step 1 :The daily demand for electricity (in millions of kilowatt-hours) in a large city is a continuous random variable with probability density function that is shown below.
Step 2 :\[f(x)=\left\{\begin{array}{ll} 0.2-0.02 x & \text { if } 0 \leq x \leq 10 \\ 0 & \text { otherwise } \end{array}\right.\]
Step 3 :The question asks for the probability that the daily demand for electricity is less than 9 million kilowatt-hours. This can be found by integrating the probability density function from 0 to 9. The integral of a probability density function over an interval gives the probability that the random variable falls within that interval.
Step 4 :\[\int_{0}^{9} f(x) d x\]
Step 5 :The result of the integration is 0.99. This means that the probability that the daily demand for electricity is less than 9 million kilowatt-hours is 0.99 or 99%.
Step 6 :Final Answer: The probability that the daily demand for electricity is less than 9 million kilowatt-hours is \(\boxed{0.99}\) or \(\boxed{99\%}\).