Question

In the above number tower, what are the values of a and b?

• A. $a=25,b=20$
• B. $a=25,b=15$
• C. $a=30,b=20$
• D. $a=15,b=25$

Answer 1

The correct option is B $a=25,b=15$



Since 5 + 10 = 15, it can be seen that the first number on the second floor is the sum of the first two numbers on the first floor.

Using this rule, we must have the sum of the two numbers on the second floor equal to the topmost number.
$\Rightarrow 15+a=40$
Therefore, to find a, we need to subtract 15 from 40.
$\Rightarrow a=40-15=25$


Similarly, we need to subtract 10 from 25 to find the value of b as the sum of 10 and b equals 25.
i.e., b = 25 - 10 = 15