If A : B = 2 : 5 and B : C = 4 : 5, then C : A = ?

1. 5 : 2
2. 2 : 1
3. 15 : 8
4. 25 : 8

Given:

A : B = 2 : 5

B : C = 4 : 5

To find C : A, first find A : C by multiplying the ratios:

$\dfrac{A}{C} = \dfrac{A}{B} \times \dfrac{B}{C} \\[1em] = \dfrac{2}{5} \times \dfrac{4}{5} \\[1em] = \dfrac{8}{25}$

So, A : C = 8 : 25.

For C : A, we reverse the ratio = 25 : 8.

Hence, option 4 is the correct option.