jj难题

hisunny

1.There are 1200 respondants to a poll, each favoring their preference
for
candidates A, B, and C. 54% favored A, 48% favored B, and 42% favored
C,
and there is 30% favored  both A and B. What is the largest possible
number
of respondants favoring C, but not C&B, nor C&A?
2.从1到N的自然数如果偶数之和为79*80，问N是多少？
这题答案是179，为什么不是178

tongxun

1\  I=a+b+c-(a jiao b)-(a jiao c)-(b jiao c) -2(a jiao c jiao b) + fei a\b\c
2\  (n-1)*(n+1)= 4*79*80