Find the fourth proportional to the numbers 100 : 50 : 40

Find the fourth proportional to the numbers 100 : 50 : 40

A 30

B 20

C 25

D Cannot be determined

Solution

Correct Answer: Option B

Let the fourth number be a.

Then, 100 : 50 : : 40 : a

i.e., 100 x a = 40 x 50

⇒ a = 4 x 5

⇒ a = 20