If an item has a constant failure rate (lambda) of 1/hour, we can model the time to failure using the exponential distribution. The probability that an item fails within a certain time (t) is given by the cumulative distribution function (CDF) of the exponential distribution, which is 1 - e^(-lambda*t). Here, lambda = 1 and t = 5. Thus the probability of an item failing in less than 5 hours is 1 - e^(-1*5) = 1 - e^(-5). The approximate value of e^(-5) is 0.00674, so 1 - e^(-5) is approximately 0.99326.