Your answer to (a) is correct. I assume for (b) the problem is that e = -b/(a/p)-b is negative and 2 is positive. Use the absolute value for the elasticity. See the second paragraph of the introduction here.
the demand for a product is f(p)=a-bp, where f(p) is quantity demanded per day and p is the price per unit sold.
a) calculate the point price elasticity: my response: please correct if is wrong: e=f'(p)(p/f(P))=-b/(a-bp/p)=-b/(a/p)-b
b) this i can not figure it out: determine the value of p that will make price elasticity of demand equal 2.
thank you
helen