A skilled worked requires at least 1010 minutes, and no more than 2020 minutes, to complete a certain task. The completion time XX is a continuous random variable with density function f(x) = c/x^2f(x)=c/x2 for 10 ≤ x ≤ 2010≤x≤20 and f(x) = 0 f(x)=0 for all other values of xx.
What is the value of cc?