X = y/3 is obtained from x: y = 1: 3.

From y: z = 2: 5, z= 5y/2.

So x: y: z =1/3:1:5/2 = 2: 6:15.

Method 2:

Because x:y= 1:3 and y:z=2:5, there is y in both ratios, while the ratio of y in the first ratio is 3 and that in the second ratio is 2.

The least common multiple of 3 and 2 is 6, so

x:y= 1:3=2:6

y:z=2:5=6: 15

So x:y:z=2:6: 15.