Evan received the following marks on her first four Math tests: 85, 71, 78, and 72. What mark must she receive on the fifth test in order to have an average mark of 78 on the five tests?
To find out what mark Evan needs to receive on the fifth test in order to have an average mark of 78 on all five tests, we can set up an equation:
(85 + 71 + 78 + 72 + x) / 5 = 78
Now, let's solve for x:
(306 + x) / 5 = 78
306 + x = 390
x = 390 - 306
x = 84
Therefore, Evan must receive a mark of 84 on the fifth test in order to have an average mark of 78 on all five tests.