Emerging data centers may host a large number of applications that consume CPU power, memory, and I/O resources. Previous studies focus on the allocation of resources in order to perfectly satisfy the demands seen in the current cycle, and the existing application placement algorithms are all based on applications. The existing application placement algorithms in literature assume that the consumption of system resources is proportional to the level of workloads submitted to the system. In this paper, we revealed that it may not be the case in some circumstances. Based on this observation, we design and implement an application placement framework, called EAPAC, for data centers. The developed framework is able to judiciously allocate to application servers a proper mixture of different types of application requests as well as an appropriate number of requests in each type. Further, we investigate the issue of resource conflicts among different applications when there exist concurrent requests in the system. We have conducted extensive experiments to evaluate the performance of the developed framework. The experiment results show that compared with the existing studies, EAPAC can improve the performance by 30% in terms of the reply rate. Especially, when there are concurrent requests in the system, the performance can be improved by 100%.