Doubt I Medium timed test (Gregmat) I Sample#9

[user3528]

Doubt in this question:

In my understanding, Quantity A should be 9/20. My logic for probability

• The total outcomes are total #gaps/spaces which is 20: Between 1-11, there are 11 numbers, but 10 gaps/ spaces; and between 1 to -9, again there are 10 gaps
• The favourable outcomes are from the left side of 0 till -9, i.e. 9 spaces/ gaps

Can you please explain why this logic is incorrect?

[cylverixxx]

Set of possible integers = \{-9, -8, -7, -6, -5, -4, -3, -2, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11\}

Set of integers that are less than 0 = \{-9, -8, -7, -6, -5, -4, -3, -2, -1\}

That gives \frac{9}{21}

@user3528

• The total outcomes are total #gaps/spaces which is 20: Between 1-11, there are 11 numbers, but 10 gaps/ spaces; and between 1 to -9, again there are 10 gaps
• The favourable outcomes are from the left side of 0 till -9, i.e. 9 spaces/ gaps

Not sure what you’re trying to do here, but my above logic should be pretty straightforward to follow.

[user3528]

Yes, your approach is very clear, thank you for explaining!