Arsenic concentration in public drinking water supplies is a potential health risk. An environmental engineer wants to compare the drinking water arsenic concentrations, in parts per billion (ppb), between metropolitan an rural areas. The engineer collects a random sample of n1 = 16 vials of drinking water from metropolitan communities and n2 = 11 vials of drinking water from rural communities. The sample mean arsenic level for the metropolitan communities is = 23.1 with a sample standard deviation of s1 = 6.1. The sample mean arsenic level for the rural communities is , = 31.9 with a sample standard deviation of s2 14.2. Calculate the value of the test statistic for the test of two independent means. Enter your answer to two decimal places. Note: there %3! is no assumption of equal variance, so you will conduct a Welch's t-test and use the formula t = n2

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