Question

From among the four alternatives given below, which number replaces the questions mark?

• A. $9$
• B. $10$
• C. $18$
• D. $23$

Answer 1

The correct option is B $10$

From first figure,

$12=\frac{49-16-9}{2}=\frac{7^2-4^2-3^2}{2}$

From second figure,

$\frac{4^2-3^2-1^2}{2}=\frac{16-9-1}{2}=3$

Similarly in third figure,

$\frac{7^2-5^2-2^2}{2}=\frac{49-25-4}{2}=\frac{20}{2}=10$.

Hence, $10$ replaces question mark.