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 74%?
M13-03.
Options
A) N−35 B) N+72 C) 2N+76 D) 2N+70 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  0.74*200= 
<gadget id="calculator"> 0.74*200</gadget>
<output>148</output>
148 correct answers, so in the second test he must get   148-70= 
<gadget id="calculator">  148-70</gadget>
<output>78</output>
78 questions correctly.   Now, plug N=1 into the answer choices to see which one yields 78. Only option D fits.   Answer: 2N+76.
<result>C</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 74%?
M13-03.