What is the smallest number that should be added to 40 so that the result is the third proportional to 16 and 28?

Correct option is B

Given:
First number = 16
Second number = 28
Third proportional = x
Formula Used:
Third Proportional Formula:
​$$\frac{a}{b} = \frac{b}{x} \\\ \\\text{Therefore, } x = \frac{b^2}{a}$$​​
Solution:
Find Third Proportional
​$$x = \frac{28^2}{16} \\\ \\28^2 = 784 \\\ \\x = \frac{784}{16} = 49 \\\ \\$$

Thus, third proportional = 49
Number to be added to 40
40 + k = 49
k = 49 - 40 = 9
The smallest number to be added to 40 is 9.