Problem Solving

Max@Math Revolution wrote:[Math Revolution GMAT math practice question]

If xy : yz : zx = 1:2:3, then what is x : y : z ?

A. 2 : 3 : 6
B. 3 : 2 : 6
C. 6 : 2 : 3
D. 6 : 3 : 2
E. 3 : 6 : 2

Let's focus on pairs of values

If xy : yz : zx = 1:2:3, then we know that xy : yz = 1:2
Take xy : yz and divide both sides by y to get the EQUIVALENT ratio x:z
This means x:z = 1:2

Check the answer choices...
A. 2 : 3 : 6 this answer choice says x:z = 2:6. We need x:z = 1:2 ELIMINATE A
B. 3 : 2 : 6 this answer choice says x:z = 3:6 (which equals 1:2) KEEP B
C. 6 : 2 : 3 this answer choice says x:z = 6:3. We need x:z = 1:2 ELIMINATE
D. 6 : 3 : 2 this answer choice says x:z = 6:2. We need x:z = 1:2 ELIMINATE
E. 3 : 6 : 2 this answer choice says x:z = 3:2. We need x:z = 1:2 ELIMINATE

By the process of elimination, the correct answer is B

Cheers,
Brent