Total case possible for throwing 3 dice independently $= 6*6*6 = 216.$
-------------------------------------------------------------------------------------------------------------
Favorable cases :
$(6,2)$ and $(1,5)$ are only possible pairs that give 4 as the difference.
Cases with (6,2) possible are
$(6,6,2)$ and these can be arranged in $\frac{3!}{2!}$ ways = 3 ways
$(6,5,2)$ and these can be arranged in $3!$ ways = 6 ways
$(6,4,2)$ and these can be arranged in $3!$ ways = 6 ways
$(6,3,2)$ and these can be arranged in $3!$ ways = 6 ways
$(6,2,2)$ and these can be arranged in $\frac{3!}{2!}$ ways = 3 ways
$\therefore$ 3+6+6+6+3 = $24$ cases possible
Cases with (5,1) possible are
$(5,5,1)$ and these can be arranged in $\frac{3!}{2!}$ ways = 3 ways
$(5,4,1)$ and these can be arranged in $3!$ ways = 6 ways
$(5,3,1)$ and these can be arranged in $3!$ ways = 6 ways
$(5,2,1)$ and these can be arranged in $3!$ ways = 6 ways
$(5,1,1)$ and these can be arranged in $\frac{3!}{2!}$ ways = 3 ways
$\therefore$ 3+6+6+6+3 = $24$ cases possible
$\therefore$ Total number of favorable cases = 24 + 24 = $48$
----------------------------------------------------------------------------------------------------------
$\therefore$ Required Probability = $\frac{Total number of favorable cases}{Total number of cases}$ = $\frac{48}{216}$ = $0.22$