If a : b : c = 3 : 4 : 7, then the ratio (a + b + c) : c is equal to

Answer: Option A

$$\begin{array}{rl}& a:b:c\\ & 3:4:7\\ & \boxed{3x:4x:7x}\Rightarrow 14x\\ & \therefore a+b+c=14x\\ & c=7x\\ & \therefore \left(a+b+c\right):c\\ & =14x:7x\\ & =2:1\end{array}$$