Only one side of the interval can fail

Suppose that the probability density function of the random variable X is $f(x)=2(\theta -x)/{\theta }^2$ if $0\le x\le \theta$, and 0 otherwise, where $\theta >0$ is an unknown parameter. Based on a single observation X, the confidence coefficient of the confidence interval [(2/5)X, (5/2)X] for $\theta$ is