DS OG12

[ss1]

Favorable Unfavorable Not Sure
Candidate M 40 20 40
Candidate N 30 35 35
124. The table above shows the results of a survey of
100 voters who each responded “Favorable” or
“Unfavorable” or “Not Sure” when asked about their
impressions of Candidate M and of Candidate N. What
was the number of voters who responded “Favorable”
for both candidates?
(1) The number of voters who did not respond
“Favorable” for either candidate was 40.
(2) The number of voters who responded
“Unfavorable” for both candidates was 10.

[ss1]

my answer:
total= Fav(m)+ f(n) - fav (both m and n)+ neither. since A gives you neither, put them all liek this:
100= 40 + 30 - x +40
x=10

the reason we reject B is that it gives us just the number for unfavorable, we have no idea what fav for both or what unsure number is.
but OG 12 has given this long explanation that i just don't understand. can someone explain this better?

[ss1]

comeon guys, please. someone answer