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The Bureau of Labor Statistics estimates the unemployment rate in the United States monthly by surveying 60,000 individuals. 
a)   In one month, 3.4% of the 60,000 individuals surveyed are found to be unemployed. Find the margin of error for this estimate.  _______________________
b)   Suppose that the number of individuals surveyed were increased by a factor of four (to 240,000). By how much would the margin of error change? _______________________
c)   Suppose that the number of individuals surveyed were decreased by a factor of four (to 15,000). By how much would the margin of error change?