diffence between efficiency and effectiveness?

Effectiveness means completing the given work in the required time. In other words, it means doing the right things with focus on the end result. 

Efficiency on the other hand, means completing the task with minimum possible costs and resources. Efficiency is said to increase if greater benefits are achieved using lesser resources or even if same benefits can be derived by cutting down on resources.

Thus, it can be said that while effectiveness is concerned with just the completion of the task in stipulated time, on the other hand, efficiency is concerned with completion of task but with minimisation of cost and judicious utilisation of resources.