Question 37

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waecmaths question: 

If the ratio  x : y = 3 : 5 and y : z = 4 : 7, find the ratio x: y : z

Option A: 

15 : 28 : 84

Option B: 

12 : 20 : 35

Option C: 

3 : 5 : 4

Option D: 

5 : 4 : 7

waecmaths solution: 

$\begin{align}  & \frac{x}{y}=\frac{3}{5} \\ & x=\frac{3y}{5} \\ & \frac{y}{z}=\frac{4}{7} \\ & z=\frac{7y}{4} \\ & x:y:z=\frac{3y}{5}:y:\frac{7y}{4} \\ & \text{Multiply through by }20 \\ & 20x:20y:20z=12y:20y:35y=12:20:35 \\ & \text{Option B} \\\end{align}$

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