17 , x , 35 ,12, y

Is the range of the 5 numbers in the list above less than 30 ?

(1) 6<= x<= 20
(2) y = 2x

Range = largest - smallest

1) x(min) = 6
Range = 35-6 I.e. < 30 if x is smaller than y. But no info on y. So can't decide.

2) x=2y, x and y could be 15 and 30 or 100 and 200 or any other pair. Nothing can be concluded on range.

Combining 1&2 x=6, y=12 is min value of x and y. Range = 30 or less
Max value of x and y is 20 and 40.
Range = 40-12+1 I.e. <30

So range has to be less than 30. Hence C

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17 , x , 35 ,12, y

Without x and y, the range is 35 - 12 = 23 which is less than 30.

(1) 6<= x<= 20

Ignoring y, if x is within 6 to 20, the range of the set will stay less than 30. Maximum range can be 35 - 6 = 29. But we don't know y. If y is 10, range will stay less than 30 but if y is 100, the range will be much higher than 30.

(2) y = 2x
We don't know the values of x and y so cannot say what the range will be.

Using both, If x lies between 6 and 20, y will lie between 12 and 40. But y will be 40 only when x is 20. Even in that case, the range will be 40 - 12 = 28. We have already seen that if x is 6 and y is 12, the range will stay below 30. In all in-between cases, the range will be below 30 only.

Answer (C)
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