13. In the figure shown, each line joining two numbers is to be labelled with the sum of the two numbers that are at its end points.
How many of these labels are multiples of 3 ?
A 10
B 9
C 8
D 7
E 6
13. A We denote the label joining $m$ and $n$ as $(m+n)$. The labels which are multiples of 3 are $(1+2),(1+5),(1+8),(2+4),(2+7),(3+6),(4+5),(4+8)$, $(5+7),(7+8)$. So 10 of the labels are multiples of 3 .