Probability, Q. 4 out of 14 of the (I’m Overwhelmed) Data Analysis Progress Quiz #9

GRE Quant Problem Solving
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Q. 4 out of 14 of the (I’m Overwhelmed) Data Analysis Progress Quiz #9

The probability of an event is 0.45
P=0.45. Which of the following values expresses the probability P?
Choices:
I: 9/20
II: 0.45
III: 9:20
IV: 4.5
V: 45

I ticked the first two choices correctly but am not too sure why 9:20 as a ratio is listed as a possible answer choice in the solution…doesn’t it imply there are 29 possibilities?

e.g.

  • 2 red marbles and 3 green marbles in a bag i.e. 5 total
  • ratio of red:green marbles would be 2:3
  • P (picking a red marble) = 2/5 = 0.4
  • The ratio of marbles is 2:3 but this doesn’t mean the probability is 2/3 (0.66…) (video suggests this line of reasoning for the answer)

Either i’m overthinking it as it’s a fairly basic concept, or perhaps I am being dumb or the question is not clear enough (or combination of all of the above lol) - thoughts?

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You are confusing different concepts.

No.

“Probability is a measure of likelihood and is the ratio of favorable outcomes to the total number of equally-likely outcomes.”

9:20 expressed as a probability is valid here.

In your marbles example, the probability of picking a red marble expressed as a ratio is 2:5 (not 2:3)

Red marble: Green Marble = 2 : 3 which implies 5 marbles in total. But that is not probability.

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Hi - thanks for replying

In essence, ratios as a probability measure is viewed as:
Favourable Outcomes:Total Outcomes

Gotcha

1 Like
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As a side note, it would be really weird if two equivalent numbers weren’t both right. Essentially, you can often evaluate equivalent expressions on their own for most questions, since the physical interpretation is usually irrelevant—except as a tool for your own problem solving.