Answer:
Option B
Explanation:
Given that garrison had provision for 3000 men for 30 days
Hence, after 10 days, the remaining food is sufficient for 3000 persons for 20 days
Remaining persons after 10 days $=3000+ 1000$ $= 4000$
Assume that after 10 days,the remaining food is sufficient for $4000$ persons for $x$ days
More men, Less days (Indirect Proportion)
$\Rightarrow Men\quad 3000:4000\}::x:20$
$\Rightarrow 3000\times 20$ $=4000x$
$\Rightarrow x=\frac{3000\times 20}{4000}$ = 15 days.
