A company sells two mathematically similar spherical balloons. The small balloon has diameter 20 cm and costs 3.50 pounds. The large balloon has diameter 35 cm and costs 9.50 pounds. The company intends the cost of each balloon to be proportional to the amount of material used to make it (its surface area).
(a)Work out the surface area scale factor from the small balloon to the large balloon.(2)
(b)Use your answer to part (a) to work out what the large balloon should cost if the cost is exactly proportional to surface area.(2)
(c)The large balloon actually costs 9.50 pounds. Comment on whether the large balloon is good value for money compared with the small balloon, giving a reason.(1)
(Total for Question 19 is 5 marks)