55% of respondents to a survey consisted of those who used both M and N and those who used neither M nor N. 47% of respondents did not use M. 40% used N. What percent of respondents used only N?	Choose the correct choice:
A) 16%
B) 21.5%
C) 20%
D) 18.5%
E) 17.5%
From the question, we can summarize the information as follows:   N Not N   M X   Not M 16%ns y 47   40 100   Then we can set a system of 3 equations 3 unknowns described below:   X + Y = 55   X + 16%ns = 40   Y + 16%ns = 47   Sum up all three equations to get 2X + 2Y + 216%ns = 142   Divide both sides by 2 to get X + Y + 16%ns = 71   Replace X + Y with 55 to get   55 + 16= 
<gadget id="calculator">  55 + 16</gadget>
<output>71</output>
71   Substract 55 from both sides to get 16%ns= 71 - 55= 
<gadget id="calculator">71 - 55</gadget>
<output>16</output>
16   The answer must be 16%.
<result>A</result>
55% of respondents to a survey consisted of those who used both M and N and those who used neither M nor N. 47% of respondents did not use M. 40% used N. What percent of respondents used only N?