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To find the mean, we need to calculate the sum of the products of each value and its frequency, and then divide by the total frequency:
Mean = (14*7 + 15*9 + 16*12 + 17*18 + 18*20 + 19*17 + 20*4) / (7 + 9 + 12 + 18 + 20 + 17 + 4)
Mean = 989 / 87
Mean β 11.35
Therefore, the correct choice is:
The mean is approximately 11.35 years.