The fourth proportional to 0.12, 0.21 and 8 is-

Solution (By Examveda Team)

Let the fourth proportional to 0.12, 0.21 and 8 be x
$$\eqalign{ & {\text{Then,}} \cr & = {\text{0}}{\text{.12}}:{\text{0}}{\text{.21}}::{\text{8}}:x \cr & \Rightarrow {\text{0}}{\text{.12}}x = 0.21 \times 8 \cr & \Rightarrow x = \frac{{0.21 \times 8}}{{0.12}} \cr & \,\,\,\,\,\,\,\,\,\,\,\, = \frac{{21 \times 8}}{{12}} \cr & \,\,\,\,\,\,\,\,\,\,\,\, = 14. \cr} $$