11. Werner wrote a list of numbers with sum 22 on a piece of paper. Ria then subtracted each of Werner's numbers from 7 and wrote down her answers. The sum of Ria's numbers was 34 .
How many numbers did Werner write down?
A 7
B 8
C 9
D 10
E 11
SOLUTION
B

For each number $n$ that Werner wrote down, Ria wrote $7-n$. Therefore, the sum of one of Werner's numbers and Ria's corresponding number is 7. Since the total of all Werner's numbers and all of Ria's numbers is $22+34=56$, the number of numbers that Werner wrote down is $56 \div 7=8$