Project managers recognise that time, cost and resource estimates must be accurate to ensure effective project planning, scheduling and controlling (Larson & Gray, 2014). (b) (c) Discuss FIVE (5) guidelines, with rationale, for developing useful work package estimates for project planning purposes. (10 marks) Explain why accurate estimates are critical to effective project management. Demonstrate the uses of estimates to further support your explanation. (10 marks) Describe and contrast the FIVE (5) top-down approach of estimating. (10 marks)