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Advice & Insight From UCAT Specialists
Probabilistic reasoning questions make up a part of the decision-making section in the UCAT. In this article I will outline how to tackle these questions.
Although most of the decision-making section of the UCAT may seem quite unfamiliar, probabilistic reasoning is a part of it that may be very similar to the probability questions that you did in your maths lessons at school.
These are the general rules to refresh your memory. I am not going to go into these in a lot of detail so if you need a detailed refresher revisit the probability topic from GCSE maths.
1) The probabilities of all the outcomes of a single situation must add up to 1 (or 100%). So, if the probability of rain is 0.4. The chance of no rain must be 0.6 because 1-0.4=0.6.
2) Probability trees can aid you when calculating the probability of multiple situations occurring. However, for time’s sake, try and determine if you can solve the question without one, this will come with practice. A probability tree would be a good idea when dealing with multiple dice throws. The one below can be used to calculate the probability of rolling even or odd numbers in two dice roles. The probability of throwing even in one throw is 3/6 which is 1/2. This is the same for odd.
3) AND rule: If you need to work out the probability of situation a AND situation b occurring, multiply both the probabilities. E.g. What is the probability of rolling two Evens? The question is asking what the probability is for rolling an even number on the first roll AND even on the second roll.
4) OR rule: If you need to work out the probability of situation a occurring OR situation b occurring, add the probabilities of a and b. E.g. What is the probability of rolling an odd and an even? At first this question may seem like just an AND question. As AND is involved so you have to multiply. However, OR is also involved. In other words, what is the probability of rolling an even and an odd OR an odd and an even?
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Now I will do 2 worked examples of questions provided by the UCAT Consortium in the free UCAT test A. Try to work through the questions yourself before looking at the solution.
Learn the best UCAT strategies and practice with reflective UCAT questions & worked solutions.
Firstly, read the question and skim through the answers. You don’t need a tree diagram for this as you don’t actually need to work out the answers and the values are easy to work with. The question states that in both hospitals there is a one in ten chance of useable machines breaking down (2/20 = 1/10). You can then work out that in hospital A, 98% of the machines are useable (100-2 =98), which is greater than the 75% in hospital B so answer D is correct.
However, if you had to work out the actual values or you just want a visual representation of the question, there are two probability trees below for hospital A and hospital B with all the relevant information to work out which hospital is better. This is an AND situation: useable machine AND no break down.