Find the mean proportional of 9 and 49.

Correct option is D

Given:
Mean proportional of 9 and 49.
Formula Used:
The mean proportional between two numbers a and b is given by:
Mean Proportional = $$\sqrt {a × b}$$ 
Solution:
Mean proportional of 9 and 49 = $$= \sqrt {9 \times 49} = 3 \times 7 = 21$$​​