Question

Find the fourth proportional 1/3,2/5and8.4

Answer 1

Let the 4th proportional be x

therefore, 1/3 : 2/5 :: 8.4 : x

1/3 8.4
or ----- = ------
2/5 x

or 5/6 = 8.4/x

or 5x = 6*8.4

or x = 50.4/5 = 10.08 Ans.