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 70%?
M13-03.  Choose one.
A) N−35  B) N+69  C) 2N+70  D) 2N+72  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  0.70*200= 
<gadget id="calculator"> 0.70*200</gadget>
<output>140</output>
140 correct answers, so in the second test he must get   140-70= 
<gadget id="calculator">  140-70</gadget>
<output>70</output>
70 questions correctly.   Now, plug N=1 into the answer choices to see which one yields 70. Only option D fits.   Answer: N+69.
<result>B</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 70%?
M13-03.