If a : b = c : d = e : f = 1 : 2, then (3a + 5c + 7e) : (3b + 5d + 7f) is = ?

Solution (By Examveda Team)

a : b = 1 : 2
c : d = 1 : 2
e : f = 1 : 2
∴ a = x, b = 2x, c = x, d = 2x, e = x, f = 2x
$$\eqalign{ & \therefore \frac{{3 \times x + 5 \times 7 + 7 \times x}}{{3 \times 2x + 5 \times 2x + 7 \times 2x}} \times 1 \cr & \Rightarrow \frac{{15x}}{{30x}} \cr & \Rightarrow \frac{1}{2} \cr} $$