In order to check whether iron ore is supplied to the specification of 62% Fe, a steel company has conducted a hypothesis test with the null hypothesis as $H_0: \mu_{Fe} = 62\%$ and alternative hypothesis $H_a: \mu_{Fe} < 62\%$. A random sample of 5 observations reveal the following grade values of the lot, 58%, 56%, 60%, 64%, 62%. The t-test statistic for the hypothesis is