Question

Find the fourth proportional of:
(i) 1/3, 2/5 and 8.4
(ii) 4 hours 40 minutes, 1 hour 10 minutes and 16 hours

Answer 1

(i) 1/3, 2/5 and 8.4
Here the 4th proportional = (2/5 $\times$ 8.4)/ 1/3
By further calculation
= 2/5 $\times$ 8.4 $\times$ 3/1
So we get
= (2 $\times$ 84 $\times$ 3)/ (5 $\times$ 10 $\times$ 1)
= 252/25
= 10.08

(ii) 4 hours 40 minutes, 1 hour 10 minutes and 16 hours
It can be written as
4 hours 40 minutes = (4 $\times$ 60) + 40 = 240 + 40 = 280 minutes
1 hour 10 minutes = (1 $\times$ 60) + 10 = 60 + 10 = 70 minutes
16 hours = 16 $\times$ 60 = 960 minutes
So the fourth proportional = (70 $\times$ 960)/ 280 = 240 minutes
So, We get,
= 240/60
= 4 hours