correct answer is: b) 4000 soldiers

Explanation

Let, The whole soldiers in the army = '1'.
According to the question,
0.25 of the soldiers died, 0.15 was injured and 0.3 was captivated.
So that, the total number of soldiers died, injured and captivated were \left(0.25+0.15+0.3\right) in the army.
\rightarrow 0.7 soldiers in the army.
Hence, number of escaped soldiers were \left(1-0.7\right) or 0.3
So that,
0.3 of the soldiers in the army =1200
\therefore 1 or whole soldiers in the army =\left(1200\times\large\frac{1}{0.3}\right)
\rightarrow 1200\times\large\left(\frac{1\times10}{3}\right) _{[remove decimal]}
\rightarrow 1200\times\large\frac{10}{3}
\rightarrow 4000
So that, there were 4000 soldiers in the army.
Ans: There were total 4000 soldiers in the army.

Other variants of this particular question are:

1. Calculate the total number of soldiers in the army when 25% died, 15% were injured, 30% were captured, and the remaining 1200 escaped.
2. Find out the initial strength of the army when 25% died, 15% were injured, 30% were captured, and the rest, 1200 soldiers, escaped.
3. Calculate the original size of the army when percentages of soldiers were lost in combat and escapees numbered 1200, after 25% died, 15% were injured, and 30% were captured.
4. What was the total number of soldiers in the army when casualties, injuries, and captures accounted for a fraction of the soldiers, and the remaining escaped, totaling 1200?