RRB NTPC Mains or Stage 2 Model Paper 10 with solutions

Concept:Solve the equation by isolating the square root and then squaring both sides.Explanation:Given: $\sqrt{?} - 11 = \sqrt{1521}$.First simplify the right-hand side: since $39^2 = 1521$, we get $\sqrt{1521} = 39$.Now the equation becomes $\sqrt{?} - 11 = 39$.Add 11 to both sides: $\sqrt{?} = 39 + 11 = 50$.Square both sides to remove the square root: $? = (50)^2 = 2500$.Check: $50 - 11 = 39$ and $39^2 = 1521$, so the value works perfectly.Now examine the options: option A is $\sqrt{2500} = 50$, which is the value of $\sqrt{?}$, not $?$ itself.Option B is $(28)^2 = 784$, and option C is $\sqrt{28}$, both clearly incorrect.Since $? = 2500$ is not directly listed, the correct choice is "None of these".Answer:The required value is $? = 2500$, so option D (None of these) is correct.