(a) Want means a mere desire for a commodity while demand is a desire for a commodity backed up by the ability and willingness to pay. Demand can also be
described as the quantities of goods that consumers are willing and able to buy at alternative prices over a given period of time.
(b) (i) A reduction in the number of consumers will lead to a decrease in demand. This will cause a shift in the demand curve to the left as shown in the diagram below. i.e. from DoDo to D1D1
(ii) When the price of substitutes increase, this will lead to an increase in the demand for the commodity. This will cause a shift in the demand curve to the right as shown in the diagram below. i.e. from DoDo to D1D1
(iii) A decrease in the price of the commodity from Po to P1 will cause an increase in the quantity demanded from q\(_0\) to q\(_1\) as shown below. This will be shown as a movement along the same demand curve.