The total number of 4 -digit numbers whose

Since, required number has G.C.D with 18 as 3 . It must be odd multiple of ' $3^{\prime}$ but not a multiple of '9'.

(i) Now, 4 -digit number which are odd multiple of ' $3^{\prime}$ are,

$1005,1011,1017, \ldots \ldots \ldots \ldots .9999 \rightarrow 1499$

(ii) 4-digit number which are odd multiple of 9 are,

$1017,1035, \ldots \ldots \ldots \ldots . .9999 \rightarrow 499$

$\because$ Required numbers $=1499-499=1000$