Estimates based on studies of the US population suggest that a 10% increase in the price of cigarettes would reduce overall consumption by adults by 3% to S%. The same 10% increase would reduce the consumption by youths by 13%. 

1. Calculate the price elasticity of demand for cigarettes among US adults and among US youths. 

2. Suggest possible reasons for the different magnitude of elasticity between the two groups. 

3. Explain two possible reasons why a government would place a tax on cigarettes.