Question

The fourth proportional to 1.2 3.9 and 2 is

Answer 1

Answer:

29.25

let fourth proportional be x,then 1.2, 3.9, 4, x

using cross product rule,

1.2×x=3.9×9

1.2×x=35.1

x=35.1/1.2

x=29.25

Answer 2

Answer: The fourth proportional is 6.5

Step-by-step explanation:  

Let the fourth proportional be x

Therefore 1.2:3.9::2:x are proportional if

Product of means = Product of extremes

 $3.9\times 2= 1.2 \times x\\\\\Rightarrow \dfrac{3.9\times 2}{1.2} =x\\\\\Rightarrow x= 6.5$

Hence, the fourth proportional is 6.5