Ok it was a tricky one.
Why do we have to consider all the values in range? I know the min and max range and I selected only those options too but my answer is incorrect

Case 1:
Consider all points lie in the same straight line. Then you have two option, 18 - 11 = 7 as minimum length, and 18 + 11 = 29 as maximum length.

Case 2:
Consider these 3 points makes a triangle in the plane. Then all the answer values between the minimum and maximum range are also valid answers.

So, correct answers should be

Here's a sketch of what we're dealing with:


This question is testing your knowledge of the following rule;
If two sides of a triangle have lengths A and B, then . . .
DIFFERENCE between A and B < length of third side < SUM of A and B


This means we can write: 18 - 11 < x < 18 + 11
Simplify: 7 < x < 29

IMPORTANT: The correct answer here WOULD be C, D, E IF we were told that points Q, R and S create a triangle.
However, since we're not told the points create a triangle, it's also possible that all three points are on the same line, in which case we can also get 7 and 29 as possible lengths of RS

For example, if all three points are on a line as follows...

... QS has length 29

And if all three points are on a line like this...

... QS has length 7


Answer: B, C, D, E, F

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