Specific Test Operations for Optiver/Tibra/Etc


Hey Folks,

So I've been practising for the mental arithmetic tests most firms make you take. With the help of a few speed/mental math books (Handley etc.) I've got a good grasp on how to do most types of questions.

However, there are some that still stump me, and I'm wondering if anyone has any insight. For instance, questions like

1. 185 * 0.48
2. 720* 0.28
3. 84*65

There's something about these numbers which leads to easy answers (e.g. the answer to 1 is 88.8) but I'm not sure what it is (is it because 0.48 is close to 0.5? Because 84 is 21 * 4)? Is there a trick to multiplying two numbers that end in five or are close to five?

They could be calculated with a pen and a pad but that would take 10 to 15 seconds and the tests only give 5 seconds or less, so..... am I missing something? Is there an on-line guide to speed math tricks I should be reading?

Any and all thoughts appreciated. Also, any guides to the 'next number in a sequence' problems? I found some sort of guide about taking the difference between successive differences but can't seem to locate it again. Anyway, many thanks, sorry if this ended up being a very long message!

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