1
a) 2~20 is the same as 1~19, therefore the answer is 19
b) 7~16 is the same as 1~10, therefore the answer is 10
c) 4~13 is the same as 1~10, therefore the answer is 10
2 Let us divide all the numbers in the set by 3:
1,2,3...14
Therefore the answer is 14.