GWD数学题请教！感谢！

melody远行

	Favorable	Unfavorable	Not Sure
Candidate M	40	20	40
Candidate N	30	35	35

The table above shows the results of a survey of 100 voters 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.
                  这道题找不着思路，有会的同学能给解释解释吗？感激不已！

melody远行

感谢!

pigman007

这是OG数学的DS第124题，如果LZ身边有OG，看下他的解释吧