14. From the 20 numbers 11, 12, 13, 14, ... 30, at least ( ) numbers must be taken to ensure that there are two numbers whose sum is a multiple of ten.
【Analysis】(11, 29) (12, 28) (13, 27) (14, 26) (15, 25) (16, 24) (17, 23) (18, 22) (19, 21) (20, 30), there are 10 drawers. By the drawer principle, selecting 11 numbers, there must be 2 numbers falling into the same drawer, and the sum of the 2 numbers in the same drawer is a multiple of ten. If taking 10 numbers, one can take $11, 12, 13, 14, 15, 20, 21, 22, 23, 24$, in which the sum of any two numbers is not a multiple of ten. Therefore, at least 11 numbers need to be taken.