If Two Random Samples of Sizes 30 and 36 Are $\bar { X } _ { 1 }$

Multiple Choice

If two random samples of sizes 30 and 36 are selected independently from two populations with means 78 and 85,and standard deviations 12 and 15,respectively,then the standard error of the difference $\bar { X } _ { 1 }$ and $\bar { X } _ { 2 }$ is equal to:

A) 0.904
B) 3.324
C) 3.391
D) 0.833