Question

What is the sum of the mean proportional between 1.4 and 35 and the third proportional to 6 and 9?

• A. 20.5
• B. 18.5
• C. 16.5
• D. 21.5

Answer 1

Answer:

A. 20.5

99^2Formula used:

Mean proportion of a and b $=\sqrt{ab}$

Third proportion of a and b $=\frac{b^2}{a}$

Calculation:

Mean proportions of 1.4 and 35

$⇒x=\sqrt{(1.4\times{35})}$

$⇒x=\sqrt{(49)}$

⇒ x = 7

Third proportion of 6 and 9 

$y=\frac{9^2}{6}$

$⇒y=\frac{81}{6}$

⇒ y = 13.5

Hence, the required sum = 7 + 13.5 = 20.5

∴ The correct answer is option (1).