After taking N tests, each containing 100 questions, John had an average of 70% of correct answers. How much does John need to score on the next test to make his average equal 73%?
M13-03. Select the correct option:  A) N−35  B) N+72  C) 2N+70  D) 2N+74  E) 2N−35
Say N=1.   So, after 1 test John has 70 correct answers.   In 2 tests, so in 200 questions he needs to have  0.73*200= 
<gadget id="calculator"> 0.73*200</gadget>
<output>146</output>
146 correct answers, so in the second test he must get   146-70= 
<gadget id="calculator">  146-70</gadget>
<output>76</output>
76 questions correctly.   Now, plug N=1 into the answer choices to see which one yields 76. Only option D fits.   Answer: 2N+74.
<result>D</result>
After taking N tests, each containing 100 questions, John had an average of 70% of correct answers. How much does John need to score on the next test to make his average equal 73%?
M13-03.