The mean proportional between 68 and 272 is:

Correct option is B

​Given:
​The two numbers are 68 and 272.
​Formula Used:
​Mean Proportional = $$\sqrt {a × b}$$​​​
​Solution:
​The two numbers are 68 and 272.
​Mean Proportional = $$\sqrt {68 × 272} = \sqrt {17 \times 4 \times 17 \times 16} = 17\times2 \times 4 = 136$$​​ 
​Thus, the mean proportional between 68 and 272 is 136.​