Abstraction: filter the essential, drop the rest

Abstraction means you deliberately set aside information that does not affect the outcome you care about. For example, when planning a train journey, you care about departure time, platform, and destination, but not the colour of the seats or the driver's name. The trick is to identify which variables actually change the answer: if you ignore the train's speed, you might miss a delay; if you include the seat fabric, you waste mental effort. In EPSO-style tasks, you often get a scenario with extra details meant to distract you—your job is to spot which details are irrelevant and which are critical.

A useful elimination trick is to ask yourself: 'If I change this detail, does the answer change?' If not, it is noise. Another hint: look for repeated numbers or names that appear only once—they are often red herrings. Also, beware of abstracting too much: if you remove the time zone from a scheduling problem, you will get the wrong meeting time. The exam often tests whether you can distinguish between essential and optional data, so practise by taking a problem and listing what you must keep versus what you can discard.

To remember this point, think of a map: a tube map shows stations and lines but not real distances or street names—that is abstraction. If you tried to include every road, the map would be useless. So, when you face a question, imagine you are drawing a map of only the necessary connections. If you can list the three or four pieces of data that truly matter, you have abstracted correctly.